test(core): add unit tests for 7 core utility modules
- executors: 13 tests, 100% coverage (init/shutdown/run_blocking/run_cpu_blocking)
- fileio_utils: 33 tests, 45% coverage (sanitize_filename, get_filename_from_headers,
calculate_crc32, create_temp_file, remove_empty_directories, create_dashboard_export,
consolidate_archive_folders)
- client_registry: 14 tests, 92% coverage (get_client, get_superset_client,
get_semaphore, get_auth_lock, shutdown)
- cot_logger: 24 tests, 100% coverage (seed/set/get trace_id, push/pop span,
structured log with markers, MarkerLogger proxy)
- encryption: 12 tests, 100% coverage (key validation, encrypt/decrypt cycle)
- rate_limiter: 9 tests, 100% coverage (ban logic, window pruning, per-IP isolation)
- auth/logger: 10 tests, 100% coverage (_mask_details, log_security_event)
busya
54a0317e98