Split the monolithic IbusEsp32 class into composable layers:
- KLineTransport: UART, GPIO ISR, ring buffers, idle detection
- IbusHandler: BMW I/K-Bus FSM, source filtering, packet callback
- IbusEsp32: thin facade preserving the original API
Library renamed from IbusEsp32 to AutoWire. Existing sniffer
sketch (main.cpp) requires zero changes. All 3 ESP32 environments
build cleanly (esp32dev, esp32-c3, esp32-s3).
