- Add test/test_kiss.cpp: Unit tests for KISS protocol encoder/decoder
Tests: frame decoding with/without escape sequences, port extraction,
round-trip encoding/decoding, signal quality encoding, buffer overflow handling
- Add test/test_commands.cpp: Unit tests for config command parsing
Tests: big-endian encoding/decoding, frequency frame parsing, type byte decoding
- Configure PlatformIO native test environment with GoogleTest framework
- Tests currently build but require linking stubs for full integration
Note: Full end-to-end testing requires mocking Serial I/O and radio functions,
which would be handled by integration tests on actual hardware or with a
more sophisticated test harness (e.g., CMake + GoogleTest).
