Expand the documentation to include details on GPIO descriptor
lookup using chip label and hardware offset, replacing the deprecated
global GPIO number approach. Added instructions for verifying the module's
version magic to ensure compatibility with the running kernel. These
updates aim to prevent common initialization and deployment errors.
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.
