Add Coverage.cmake with gcovr integration, detecting Clang vs
GCC and wrapping llvm-cov gcov in a build-dir script to handle
paths with spaces on Windows. Update README and AGENTS.md with
the new one-command-per-block documentation rule.
Replace log_message with log_debug/info/warn/err and a level filter
controlled by logger_set_level. Extract the printf sink into
log_write so CMock can intercept it in test_logger. Add 9 tests
covering emit and suppression behaviour per level.