Introduce `DEBIAN_SUITE` as a configurable argument in the Dockerfile, build
script, and CI workflow to align kernel builds with the target Raspberry Pi
OS release. Updated documentation to clarify the relationship between
suite versions and kernel compatibility.
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.
