Rename spo2_protocol target to spo2_protocol-lib, use FetchDependencies, gate demo executable
- Replace manual FetchContent blocks for crc and c_helpers with the new FetchDependencies module and fetchdependencies() calls
- Add LIB_DEMO_ENABLE option (default OFF) to conditionally build the demo executable
- Drop -Wall -Wextra -Werror, if(TARGET ...) guards, unused ASM language, and redundant enable_language(C CXX ASM) call
- Update project.yml.in to reference libc_helpers-lib.a and libcrc-lib.a
- Rename README build targets to spo2_protocol-zip_docs and spo2_protocol-zip_reports; document LIB_DEMO_ENABLE and update doc-generation command
- Pass -DLIB_DEMO_ENABLE=ON in CI docs job CMAKE_ARGS