Apply SX1262 register 0x8B5 patch for improved GC1109 RX sensitivity

[weebl2000]

Summary

• Apply undocumented SX1262 register 0x8B5 patch (set LSB=1) on Heltec V4 and Wireless Tracker V2 boards with the GC1109 FEM
• Patch recommended by Heltec engineer (@Quency-D) based on Semtech guidance
• Guarded by USE_GC1109_PA so only affects GC1109 boards

Background

Testing in MeshCore PR #1398 showed this register patch significantly improved RX sensitivity on the Heltec V4, reducing packet loss from ~55% to ~25% — bringing it in line with a RAK4631 reference node at the same location.

The patch was originally identified via discussion in meshtastic/firmware#9029 and MeshCore PR #1249.

Test plan

• Flash Heltec V4, verify RX sensitivity improvement via RSSI/SNR comparison with a reference node
• Verify TX still works correctly
• Verify no regression on other SX1262 boards (patch is behind USE_GC1109_PA guard)

[compumike]

@weebl2000 Did you have to do anything special to get this to compile? I tried and it looks like RADIOLIB_GODMODE or RADIOLIB_LOW_LEVEL flags are needed to get at lora.readRegister / lora.writeRegister:
https://github.com/jgromes/RadioLib/blob/87bf5785a3ca58dae184cff7b9860bef84a09b5c/src/modules/SX126x/SX126x.h#L826-L837

(I don't think any of the CI builds would catch this because none have USE_GC1109_PA defined.)

[weebl2000]

@weebl2000 Did you have to do anything special to get this to compile? I tried and it looks like RADIOLIB_GODMODE or RADIOLIB_LOW_LEVEL flags are needed to get at lora.readRegister / lora.writeRegister: https://github.com/jgromes/RadioLib/blob/87bf5785a3ca58dae184cff7b9860bef84a09b5c/src/modules/SX126x/SX126x.h#L826-L837

(I don't think any of the CI builds would catch this because none have USE_GC1109_PA defined.)

I haven't tried to compile this on meshtastic. Thanks. Modified the code now to use higher level function to set the register value - this should work now.