Rename library target from "fw_update_protocol" to "fw_update_protocol-lib" , gate demo executable
- Replace manual FetchContent blocks for c_helpers and endianness with FetchDependencies module
- Add LIB_DEMO_ENABLE option (default OFF) to gate the demo executable
- Drop -Wall -Wextra -Werror, if(TARGET ...) guards, redundant enable_language(C CXX) call
- Updated project.yml.in
- Pass -DLIB_DEMO_ENABLE=ON in CI docs job CMAKE_ARGS