Rename w25qxx target to w25qxx-fw_lib, adopt FetchDependencies, gate demo executable
- Replace manual FetchContent block for c_helpers with FetchDependencies module
- Drop -Wall -Wextra -Werror, if(TARGET ...) guard, and redundant enable_language(C CXX ASM) call
- Updated project.yml.in
- Pass -DLIB_DEMO_ENABLE=ON in CI docs job CMAKE_ARGS