sensor loop assumes value(index) value is ok
ref. #2543

move all checks to pre(), value() returns pre-read value
- tick() and pre() are allowed to fail specific device
- pre() would fail the sensor if any of devices fail
- value(index) is never reached unless tick() and pre() succeed

One namespace for sensor functions and types.
Fix discrepancy between topic and indexed topic funcs.
Energy types fixes, make sure we use known ratios.

Sensor fixes, moving certain pin settings and defaults into the sensor
classes, using those in the actual sensor init code.
Energy is still within the sensor module, pending version bump before moving.

simplify the internals and allow to use multiple instances

possibly fix comparison issue with raw int vs. float, when checking for
errors. division may not actually succeed

- remove 'local' index and replace sensor code depending on it with the
  existing 'slot' aka 'magnitude index' used in value() and type()
- common method to store and retrieve ratios for voltage, current,
  active power and energy. default implementation is no-op, sensor
  should implement ratio adjustment & calculations to use 'slot' indexes
- re-implement 'expected' values ui. display the actual ratio values,
  and have a separate page for updating them in a more apparent way
- remove legacy settings that were adjusting expected values
- remove legacy settings that were resetting ratios and analog calibration
- generic webui action caller, add ratios and analog calibration resets

all of 'emon' sensors were updated to utilize the new approach to the
ratio handling. pulsemeter is somewhat an outlier, but it is unclear
whether removing the energy ratio is justified

terminal part was also updated
- implement `expected` command that hooks into the new ratioFromValue
  (and what webui uses to calculate ratios)
- implement `energy` command to list only MAGNITUDE_ENERGY
- remove old pzem004t commands doing ratio reset and total energy count

another global update is related to espurna::duration
- rework module-local heartbeat and led durations into a global
  espurna::duration
- update sensor internals to use specific units instead of multiplying things
  on line-by-line basis. export count() to the api

- shrink utils source file, move heartbeat and boot management into system
- improvise with 'heartbeat' functionality. include scheduler implementation that will
manage the per-module heartbeat callbacks with individual 'mode' and
'interval' settings. current ones are mqtt (including relays, lights, thermostat), debug and
influxdb. preserve heartbeat NONE, ONCE and REPEAT, REPEAT_STATUS is effectively a hbReport & status bit.
- mqtt heartbeat is managed through mqttHeartbeat() callbacks
- tweak mqtt callbacks to use lists instead of the vector, slighly reducing the size of the .bin
- update WebUI, include report setting and update hbMode values
- make sure general.h settings include new heartbeat,
move constant definitions outside of the header
- correctly include dependencies through the .cpp, avoid leaking
internal details.
- as a side-effect, base headers are no longer included recursively

- gpio module now tracks the known providers (right now, hardware and mcp expander)
- refactored relay struct to use 'Provider' implementing setup,notify,change,boot instead of just BasePin actions
- refactored button module to use gpio provider instead of referencing types itself
- removed dual & stm code from buttons, migrate both to relay module
- added status notify and change callbacks for relayStatus (i.e. 'notify' when relay status was called, but not changed. and 'changed' when it did)  
- relays runtime configuration keys
- relay command now shows configured relays and current & target statuses
- refactor the code using relayStatus(0, blah) under LIGHT_PROVIDER check to use lightState instead
- remove rfbridge code form relay module. implement through a basic state listener in the rfbridge module, depend on RELAY_SUPPORT
- allow to bind rf codes to real relays
- drop tuya-specific lights provider, remove tuya code from relays and lights modules
- integrate tuya via relay listeners and providers, use lights custom provider
- implement channel transitions for tuya. disabled by default, and transition time and step are overridden to 2000 + 100. needs to be set to some value below the total time (i.e. `total transition time / step time == number of steps`, we need to figure out a correct time that serial comms could handle)
- lights custom provider (global, not per-pin) and state listeners
- remove lights code from relay module. implement through providers & listeners in the lights module, depend on RELAY_SUPPORT
- lights per-channel relay provider (unused atm), depend on RELAY_SUPPORT
- refactored channel transition - calculate step only once, make sure time + step values are sane, generate quick transitions with very small delay (10ms hardcoded) for transitions during OFF state i.e. we no longer waste 500ms (or whatever transition time is set to) on boot doing nothing
- transition time + step parameter for the lightUpdate
- report mask parameter for the lightUpdate
- minor fixes across the board

resolve #2222

resolve #2310

* emon: configure ratios without reboot

* settings: serialize() support

* debug: use vsnprintf from newlib, not from sdk

* settings/experimental: show defaults via `get`

* emon: override base methods, fix defaults

* sensor/emon: expose internal index calculation

- refactor configuration to use the correct index when accessing indexed
  sensor methods. store index value on magnitude, refactor loops to
  accomodate this new functionality
- rename slot(index) -> description(index), since we use 'slot' as
  numeric value

- Update sensor classes to support a generic way to store energy values
- Update sensor conversion code to deal with units and not magnitudes
- Add magnitude<->unit for sensors, generic way of defining used unit. Convert from sensor magnitude unit to the one used for display.
- Reset energy value based on index through external means (MQTT, HTTP)
- Rework energy timestamping, update webui with 'last saved' value

While this solves the energy conversion issues and we are finally seeing the real value, what I don't really like:
- KilowattHour and WattHour are separate enum tags, thus sort-of are different types altogether
- Conversion code in Energy object should probably use some generic 'ratio' calculation? (https://en.cppreference.com/w/cpp/numeric/ratio/ratio)
- We are still using runtime checks to do calculations and depend that sensor outputs only one specific value type.

Consider this a fix for energy display / storage and preliminary work on sensor.ino
Further sensor refactoring... soon.

* Add support for read PIO-A of DS2406

* Verify reset() reseult

* Sensors: refactor configuration

- move sensor implementaion to the .ino,
  remove dependency undef / define from sensor files
- update test/build/sensor.h from SENSOR_SUPPORT
- allow to change sensor config variables externally
- `#include <...>` for global headers and libraries,
  fix relative path for math library

* add missing sns <-> i2c dependency

* ledrelay should return relay_none as default

* rollback to original test header

* include debug header when requested (relative)