Add native Ethernet support for RAK4631 repeater, room server, and companion

Add W5100S Ethernet adapter support for RAK4631-based firmware, enabling
TCP CLI access on port 23 as an alternative to BLE/Serial connections.

- New SerialEthernetInterface for nRF52 with DHCP, reconnection handling,
  and shared WB_IO2 power pin management with GPS module
- Ethernet build targets for repeater, room server, and companion firmware
- Prevent GPS from toggling WB_IO2 when Ethernet module is active
- CI build check for all three ETH firmware targets

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/helpers/sensors/EnvironmentSensorManager.cpp

@@ -628,6 +628,13 @@ void EnvironmentSensorManager::rakGPSInit(){
 
 bool EnvironmentSensorManager::gpsIsAwake(uint8_t ioPin){
 
+  #if defined(ETH_ENABLED) && defined(RAK_BOARD)
+    if (ioPin == WB_IO2) {
+      // WB_IO2 powers the Ethernet module on RAK baseboards.
+      return false;
+    }
+  #endif
+
   //set initial waking state
   pinMode(ioPin,OUTPUT);
   digitalWrite(ioPin,LOW);