trying to fix #2343
*** [.pio\build\$PIOENV\firmware.bin] TypeError
`expected str, bytes or os.PathLike object, not Dir' trying to evaluate `${__get_flash_size(__env__)}'

as it turns out, PIO platform internals (sometimes) did not use the correct ldscript path

vector will not copy when move ctor is marked noexcept
remove the copy ctor 'trick', re-add dtor. explicitly do the thing we want
(...clang-tidy would've shown this issue, something to do in the CI...)

see 69c65a6a40 (commitcomment-42008295)
Because of the way DHCP is integrated into the Core logic, we need to
call wifi_softap_add_dhcps_lease(...) inbetween WiFi.softApConfig(...) and WiFi.softAp(...)

- magnitudes vector grows by calling copy ctor, ensure filter never gets deleted
- ensure we can't use magnitude member instead of ctor arg
- more magnitude references instead of using index access
- additional checks for isnan, fix report never triggering
- drop event callback. at least for EventSensor, we already have
  report with min / max value change triggers

- BaseFilter must have virtual dtor
- magnitude object is not trivial, we need to manage filter lifetime
- Ensure move also moves filter object
- Clean-up using magnitude object by value in functions

- (experimental) provide generic way to read magnitude values
- expose /api/metrics with values formatted specifically for prometheus, with relay and sensor data
- small tweaks to sensor init

Example config:
```
scrape_configs:
  - job_name: 'espurna'
    metrics_path: '/api/metrics'
    params:
      apikey: ['apikeyapikey']
    static_configs:
      - targets: ['espurna-blabla.lan:80']
```
Where ESPurna side has
```
apiKey => "apikeyapikey"
apiEnabled => "1"
```

plus, hide both under `#if RELAY_SUPPORT`

Ensure we step +1 char into the string
Ensure hex decoding of the payload ignores the separator + number of repeats

* rfb: fix unused repeats setting
* rfb: rename TIMES -> REPEATS
* rfb: use out as first arg

ref. https://travis-ci.com/github/mcspr/espurna-nightly-builder/jobs/378203413#L698

> +env ESPURNA_FLAGS=-DGENERIC_ESP01_512KB ESPURNA_RELEASE_NAME=generic-esp01-512kb ESPURNA_BUILD_SINGLE_SOURCE=1 pio run -e esp8266-512k-base -s -t release
> /home/travis/.platformio/packages/toolchain-xtensa/bin/../lib/gcc/xtensa-lx106-elf/4.8.2/../../../../xtensa-lx106-elf/bin/ld: .pio/build/esp8266-512k-base/firmware.elf section `.irom0.text' will not fit in region `irom0_0_seg'

Remove ~90Kb from the build.

- cache received rfbridge codes in the internal list, allow to operate on it via the rpn operators
- add `<N> <proto> <code> rfb_match`, matching when we receive specified protocol + code string at least N times
- add `<proto> <code> <proto> <code> rfb_sequence`, checking if specified protocol + code pairs happen in sequence
- add `<TIME> <N> <proto> <code> rfb_match_wait` - similar to `rfb_match`, but waiting for at least `TIME` (ms) via oneshot runner
- add `<proto> <code> rfb_info`, pushes code's latest timestamp and it's counter on the stack
- add `<proto> <code> rfb_pop`, which removes the specified protocol + code from the internal cache
- fix MQTT skip setting making RPN variables absent on initial connection
- default to no skip when receiving MQTT
(small issue still stands with us having non-clean MQTT session, broker will persist variable subscriptions even after unsubscribe event)

ref. 6af2bad123
2.3.0 is still not supported, but at least buildable

ref.
https://github.com/Portisch/RF-Bridge-EFM8BB1/wiki/0xA2 (desc: Learning OK)
https://github.com/Portisch/RF-Bridge-EFM8BB1/wiki/0xA3 (desc: Learning failed)
were used, but the pages did not reflect the actual implementation:

af1bddb3d8/inc/uart.h
...
RF_CODE_LEARN_KO = 0xA2
RF_CODE_LEARN_OK = 0xA3
...

- no need in template when size set as constexpr
- remove size param completely, deduce size based on buffer

- queueing efm8bb1 msg, pass around array as reference since the size is fixed
- make use of learn timestamp

- for some reason we were never checking it's output
no need to increase +1 since we write the exact number
- allow hexEncode output be decoded, enforce even-ness
- raw msg must have at least 3 bytes - start+code+end

- RF_... -> RFB_...
- rework rcswitch integration, support variable length payload
- rework rfbridge parser (not tested)
- rework settings scanning routine when trying to match rf payload
  with the relay ID
- update build tests

resolve #2326

As this is no longer an option since PIO 4.4.0
ref.
04694b4126
https://docs.platformio.org/en/latest/core/history.html

*...I have known you for so long
When we ran in circles...*