Log the current working directory in `build-in-docker.sh` to improve the
debugging process during kernel module compilation. This update helps
track the build context path passed to the Docker container.
Replace legacy gpio_to_desc() with GPIO descriptor resolution by chip label
and hardware number, ensuring compatibility with kernels using non-zero
gpiochip bases. Added `selftest.sh` for non-persistent module testing, which
performs a hardware self-test and verifies wiring before connecting the real
bus. Included a detailed README.md documenting the self-test process.
