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>