fix(telemetry): temperature UNIT conversion when temperature has decimals

[frankiearzu]

Fixes #4723

Summary of changes:

1. Fixes converting from C to F (and vice versa) when the Temperature has decimal places.
2. Optimization: Remove loop to do 10^n, and use a table "Power10[n]" to change from one Prec to another.
3. Optimization: Only do the conversion if needed, i.e, Different UNIT or different Prec
4. Move the exception of not displaying "Precision" on 3 different GUIs when sensor is UNIT_FARENHEITH to a single share code by all GUIs. TelemetrySensor::isPrecConfigurable() is only used for this UI purpose, nowhere else.

Left the Precision not been configurable when sensor is UNIT_FARENHEITH, (same behavior as before). I think this is because is already granular enough compared to UNIT_CELSIOUS.

Examples: Using LemonRX Gen2 who has a temperature sensor embeded.

NOTE: Temp was increasing while taking the screenshots.. that's why the little difference.

[frankiearzu]

@pfeerick DONE! sometimes im surprised of finding this bugs after the code been like that for so many years, Was more exposed recently that in DSM automatically convers the units to METRIC or IMPERIAL (for display) depending on the radio configuration (something missing in many other protocols.. will add a chore for this).

[pfeerick]

Yeah, some the bugs leave you scratching your head... clearly no-one used those combinations + thought to report it + someone actually bothered to try and fix it 🤪 ... it's like the "Adjust GV" long enter bug that was fixed the other day... it's been there some 6-7 years for all X7 navigation radios... yet it survived all this time... 🤪

[pfeerick]

Thanks for this... sorry it took so long to get around to it. I see what you mean with the decimal conversion i.e. 0.0 and 0.00 was completely wrong. LGTM with AFHDS2A and DSMX receivers (with internal/additional temperature sensors).