MAGIC value for powerReason should be stored in RTC backup on Horus (#7096)

- Allows the radio main application to start correctly when coming from an app in RAM
- Refactoring of the `UNEXPECTED_SHUTDOWN()` process
- Saves the RTC battery as BACKUP RAM is not needed on normal shutdown
- On PWR OFF on an ALERT, the radio won't show the next alert before shutting down
- Bootloader flashable through the SD Manager

radio/src/tasks.cpp

@@ -189,7 +189,7 @@ TASK_FUNCTION(mixerTask)
       DEBUG_TIMER_STOP(debugTimerTelemetryWakeup);
 
       if (heartbeat == HEART_WDT_CHECK) {
-        wdt_reset();
+        WDG_RESET();
         heartbeat = 0;
       }