also queue fallback check instead of resolving it in the timer
resolve #2571

c/p PSTR attribute from Core files
dostring declaration with a macro instead of a scary looking boilerplate

saves varying amount of code space, mostly deals with our key and cmd strings

* globally accessible system timer class; help out with our internal
  scheduling by always using strongly typed duration and dynamic
  time adjustment for durations longer than system limits
  (see `os_timer_t` documentation)
* our own class for scheduled callbacks which are either choosing a
  simple function pointer or std function wrapper, depending on the type
  passed into the constructor. specifically for scheduled functions,
  this allows us to filter globally scheduled functions and push them to
  the front of the queue when necessary to ensure certain order of calls
* replace Ticker instances with SystemTimer
* allow types {h, cpp} in unit tests

- clean-up comparison routines and get rid of most of the casts
- reduces total number of calls to terminalRegisterCommand
  replace with a func accepting list of commands, which in
  turn get instantiated as constexpr PROGMEM arrays
- reduce ram fragmentation, since we don't need to alloc as much
- reduce flash consumption b/c of lambda -> standalone func conversion

blockingDelay uses inverse logic; passed function should return false
when the condition is satisfied
only broken on 2.7.x, 3.x.x skips the check

get rid of board module, replace with system calls for hostname, board
and password. move boot (quirks) handlers to system as well
espurna::build { ... } namespace for our app const values

make our string comparisons nicer
also clean-up namespaces for storage access

rework more namespaces to use `espurna` root
makes internal references much easier (and shorter)

view class is not specific to settings, could use it across the app
remove duplicate code from IR

Settling on naming 'options' for enumerations (...possibly, everything
else in the future, would that make sense to store for 'setting' object)

Update terminal commands that were reporting status to also report a
full list of 'indexed' settings for the specific entity
Also updates the WebUI outputs which are (hopefuly) are already handled
as-is through the .js processing pipeline and the .html properties
receiving certain special string values

More namespacing and save ~2KiB of RAM by reducing the amount of loaded keys strings
However, ROM side of things may suffer b/c of template specializations for the
generic conversion functions when there are many different types involved.

Make sure we seamlessly handle 'convert' for the number and the string version.
And since it is a two-way map, update 'serialize' to use it as well instead of
either a simple static_cast<int> or duplicating the same strings used in 'convert'

Only string literals or static vars can be used in constexpr context,
but those can still be shoved into the flash region via PROGMEM.
Notably, PSTR(...) inside of a lambda is not a constexpr.

Some quirks to work out
- we don't 'enumerate' things through compiler, enum values may go
  missing since it is not a switch-case
- 'get' default value via query still requires us to know the settings
  key in the first place. and it still needs an explicit call to
  'serialize'
- sensor units are stringified as their display value.
  but, this also avoids two different 'string' versions of those
- EnumOptions struct instance may also be in PROGMEM, but one needs
  to be very careful to only allow aligned access to it's members
  (which currently means we can't use 8bit or 16bit 'enum class'es)

Localize build constants & settings use, no need to prefix where
namespacing already does this (and also removes some duplicates)

Make sure it could be moved further along, and the values inside of it
can be safely moved as well.

Also fixup commands that were missing ctx in OK / Error.

For this, keep things as milliseconds (at least for now)

Make sure to use __builtin_strlen in constexpr context
Remove `has*()` functions that are no longer used

Update WebUI callback to use EnumerableConfig

```
In file included from espurna\espurna_single_source.cpp:62:
espurna\wifi.cpp:282:38: error: specialization of 'T settings::internal::convert(const String&) [with T = IPAddress]' after instantiation
  282 | IPAddress convert(const String& value) {
      |                                      ^
```

given that relay, button and led settings may be hardcoded,
explicitly remove from -core and -core-webui
restore telnet debugging though, since the terminal output needs it

for -core-webui, disables mdns and the generic webui server + webui blob
per 56f74cfe, make the resulting .bin even smaller

ref. #2476

Value init Mac array, both compiler versions support this.
Named constants for conversion function lengths / sizes.

For when scanning is disabled. Remove uniqueness requirement, since
settings may contain multiple SSID with different BSSID values.

wifi::Mac conversion helpers for both xxxxxxxxxx and xx:xx:xx:xx:xx:xx

Generate initial connection list with all suitable networks, not only the best ones.
When scanning for a better network, remove results with worse rssi.

Don't remove extra scan results in the delayed scan function,
allow consumer to filter by itself.

Just `if (version < N)` instead of `if (version && (version < N))`
Fix existing functions that were not checking for `version > 0`

Immediatly try to connect when reloading settings and previous attempt
had failed. Because of locking, previously this caused a soft-lock of the
internal loop that required waiting for the long Reconnect timeout to
expire first.

Refactor the module to include namespace { ... } and move build settings into .cpp
Saves ~1.5Kb and also allows gcc to issue unused warnings for declared functions.

As a side-effect of refactoring, (temporarily?) remove softAp leases support.
Current Core moved dhcps support into a C++ code, forcing internal logic
to reference a specific object. Better to wait a bit until that
stabilizes and try again. Plus, it is not currently available in the esp-idf.

Refactor WebUI:
- remove jquery dependency from the base custom.js and use vanilla JS
- remove jquery + jquery-datatables dependency from the RFM69 module
- replace jquery-datatables handlers with pure-css table + some basic cell filtering
  (may be incomplete, but tbh it is not worth additional 50Kb to the .bin size)
- introduce a common way to notify about the app errors, show small text notification
  at the top of the page instead of relying on user to find out about errors by using the Web Developer Tools
- replace <span name=...> with <span data-settings-key=...>
- replace <div> templates with <template>, disallowing modification
  without an explicit DOM clone
- run `eslint` on html/custom.js and `html-validate` on html/index.html,
  and fix issues detected by both tools

Streamline settings group handling in custom.js & index.html
- drop module-specific button-add-... in favour of button-add-settings-group
- only enforce data-settings-max requirement when the property actually exists
- re-create label for=... and input id=... when settings group is
  modified, so checkboxes refer to the correct element
- introduce additional data-... properties to generalize settings group additions
- introduce Enumerable object to track some common list elements for
  <select>, allow to re-create <option> list when messages come in
  different order

Minor fixes that also came with this:
- fix relay code incorrectly parsing the payload, causing no relay names
  to be displayed in the SWITCHES panel
- fix scheduler code accidentally combining keys b/c of the way C parses
  string literals on separate lines, without any commas in-between
- thermostat should not reference tmpUnit directly in the webui, replace with
  module-specific thermostatUnit that is handled on the device itself
- fix index.html initial setup invalid adminPass ids
- fix index.html layout when removing specific schedules

Referencing currently used code for the NONOS, plus some Core-specific
things to handle lwip1.4 <-> lwip2 layer

Saves a bit of code handling Arduino WiFi Shield compatibility,
which we don't really need

Or, at least try to.
wifi_station_disconnect() queues the event, but receiving it will confuse the
connection loop waiting for the one right after wifi_station_connect()

Event SSID is the last connected one, reason is REASON_AUTH_FAIL (202)
Simply switch contexts to allow the event handler to run.

Plus, it's not really a constexpr in this context

SDK status is an unreliable source of info even when connecting.
Make sure to register both GotIp and onDisconnected and wait for the
events in the wait-loop, checking which one arrived first.

Plus, make sure the connection task object was actually created, before
proceeding with the connect-loop.

- reduce info lines on boot
- more compact `info` command. show versions, modules and crash info when there is one
- add `storage` command to display flash layout (experimental)
- display full chip id aka MAC, including the oui
- fix telnet never printing the crash data b/c telnet in not yet authorized
- fix eeprom size not reflecting the space used by the backup sectors
- use static flash strings when possible for the fw info

Perform actual checks in the connect() method.
Make sure empty SSID, too-big SSID, too-small or too-big passphrases fail it and force a retry.
Fixes the comment that claimed the WiFi.begin() result was checked...

Local copy of the ::begin, since it is easier to work with the SDK API directly.

- more static flash strings and flash string formats
- println() will write \r\n when we mostly just use the \n
(and avoid mixing it up in the same function)

- replace JustWifi with a custom WiFi module
- re-implemented Core methods that deal with scanning, directly work with the SDK callback
- re-implemented Core method for opmode to avoid dealing with the 2.7.x pseudo modes
- re-implemented Core method for forced-(modem)-sleep (with the intention to merge with OpmodeNull... todo)
- disable reconnect and autoconnect from SDK, avoid unintentionally storing ssid & pass for these and
  make connection routine watch for events instead. timeout is implemented as a local timer
- do not store runtime data that can be retrieved via SDK calls
- settings are loaded only when starting AP or STA, networks are no longer kept in memory
- settings STA ssidN must be unique
- remove char buffer from the event callback
- trigger station-disconnected event when actually disconnected, not when connecting or explicitly requesting it
- generic rssi sorting method for initial connection, do rssi checks while connected to find a better network

Drop (temporarily?) wps and smartconfig. Both are implementable with the new approach,
but come with some weird expectations from the SDK side (no extra heap with wps, broadcasting plain-text
passphrase with smartconfig, storing station config implicitly, etc.).

Both are sort-of fixed with RTOS SDK, but it is still a big question of whether to support them at all in the current state.