[AlexandrTyshchenko]

Problem

With agc.reset.interval > 0, Dispatcher::loop() calls resetAGC() on a fixed timer
(restarted only after a TX). Each reset puts the radio into warm sleep, recalibrates and
re-arms RX, so the node is deaf for that time. On a busy channel this costs packets every
interval, although the gain cannot be stuck: packets are still being decoded.

Change

When the AGC timer fires:

• skip the reset if a valid packet was received within the last reset interval
  (the gain is fine), or if a packet is queued for transmit;
• reset anyway at least once per AGC_FORCED_RESET_MILLIS (default 24 h, overridable
  build flag), and on the first tick after boot;
• otherwise reset as before.

"Valid packet" means one that passed tryParsePacket() (set right after logRx()), so
corrupt/garbage receptions don't count as hearing.

This is the same logic Meshtastic uses on develop
(RadioLibInterface::periodicRadioMaintenance(): check every 60 s, reset only if nothing
was decoded for AGC_IDLE_RESET_MS = 60 s, forced every AGC_FORCED_RESET_MS = 24 h,
never with TX queued). Here the idle window is the configured agc.reset.interval itself.

Nodes with agc.reset.interval 0 (the default) are not affected. MESH_DEBUG builds log
each decision (AGC reset / AGC reset skipped, last rx N ms ago / ... tx queued).

Testing

ProMicro nRF52840 + E22-400M22S (SX1268), repeater, MESH_DEBUG, agc.reset.interval 8:

• quiet channel: reset every 8 s;
• adverts received at t and t+6 s: the next two resets skipped
  (last rx 923 ms ago, last rx 1673 ms ago);
• after 8 s with nothing received: resets resumed;
• no RX/TX errors; the node has since run with agc.reset.interval 60.

Builds: ProMicro_repeater, RAK_4631_repeater, Heltec_v3_repeater.

Not tested: the 24 h forced reset (logic only), and the "TX queued" branch was not hit
in the bench run.

Notes

• fix: add zombie radio recovery for TX fail reset and RX stuck reboot #2151 changes the same call to forceResetAGC(); the two are independent and would
  merge with a trivial conflict.
• Related: SX126x AGC reset: wait for calibration before re-writing registers #3749 (calibration wait inside the SX126x AGC reset), Fix/noise floor ratchet, adapt noise to the real floor with recovery in both directions #2933 (noise floor after
  the reset).