- Introduce a `shutdown_acknowledged` flag with supporting mutex and condition variable for safe thread shutdown.
- Ensure logger thread signals shutdown acknowledgment before exiting.
- Update cleanup process to properly destroy new synchronization primitives.

… async logging

- Store `journal_direct`, `journal_libsystemd`, and `syslog` initialization states during enqueue to ensure consistent behavior during logging.
- Add fallback mechanisms for logging to `stderr` when target destinations are not initialized.
- Introduce a flush operation before log destination reinitialization to avoid losing pending log messages.
- Refactor logging queue thread signature and improve error handling for asynchronous journal and syslog writes.

…lized send logic

- Introduce `nd_logger_journal_format` for consistent journal native protocol (KEY=VALUE\n) formatting.
- Update to use `journal_direct_send` for improved handling and fallback mechanisms.
- Simplify `nd_logger_journal_direct` by separating formatting and sending responsibilities.

- Replace the legacy `nd_log_queue` structure with the `nd_log_event_loop` and `nd_log_cmd_pool` architecture for cleaner and more efficient log entry processing.
- Transition from a queue-based logging system to a command-driven event loop using uv_async callbacks.
- Introduce reusable command pool with support for opcodes (e.g., `ND_LOG_OP_ENTRY`, `ND_LOG_OP_FLUSH`, `ND_LOG_OP_SHUTDOWN`) to enable more flexible event-driven log operations.
- Simplify logging thread to focus on processing commands in an event loop, improving modularity and reducing synchronization complexity.
- Update public API to reflect the new architecture, including changes to queue management, shutdown logic, and entry enqueueing.

- Remove unused initialization fields (`journal_direct`, `journal_libsystemd`) from log queue entries to reduce enqueue-time complexity.
- Replace raw buffer handling with `CLEAN_BUFFER` to streamline memory management and auto-free resources on return.
- Adapt async file logging to look up `FILE*` at write time, enabling proper log rotation handling.
- Deprecate journal async logging support due to sync path optimization.
- Introduce timed shutdown wait with fallback to prevent indefinite hangs during logger thread termination.

- Prevent async logging for fallback `FILE*` mismatches to avoid message loss.
- Add atomic flag signaling for immediate shutdown when the queue is full.

…R` remapping to `NDLM_FILE` during `select_output`.

- Add atomic queue depth decrement during entry processing.
- Prevent memory leaks by freeing allocated buffers when enqueueing is skipped.

…ocated log messages.

- Add source index bounds check to prevent out-of-bounds access during log entry processing.
- Optimize command pool cleanup by iterating between active indices instead of full range.
- Refactor initialization function to ensure thread-safe single execution using `FUNCTION_RUN_ONCE`.
- Enhance shutdown logic to safely handle completion destruction after thread termination.
- Use CAS loop for accurate high-water mark updates in concurrent scenarios.
- Adjust async signaling to prevent race conditions during shutdown.