Add variant configuration for M5Stack Unit C6L (ESP32-C6, SX1262 LoRa,
SSD1306 64x48 SPI display). Includes:
- Board class with PI4IO I/O expander for LoRa RF control
- DIO flash mode fix for ESP32-C6 bootloader compatibility
- SSD1306 SPI display with custom minimal UITask for 64x48
- CustomSerialBLEInterface fix for correct BLE Connected status
- All 4 firmware environments: companion (USB/BLE), repeater, room server
* BasChatMesh: new onContactRequest(), for PAYLOAD_TYPE_REQ handling.
* companion, repeater and room_server: now with basic 'plumbing' to handle REQ_TYPE_GET_TELEMETRY_DATA (0x03).
* dependency: added CayenneLPP to libdeps
* all target.* modules now with a stub 'sensors' object.