This commit introduces a new ThreadPool class that provides efficient worker
thread management for background tasks. Key features include:
- Dynamic scaling from min to max threads based on workload
- Proper database connection management in multisite setup
- Graceful shutdown with task completion
- Robust error handling and logging
- FIFO task processing with a managed queue
- Configurable idle timeout for worker threads
The implementation is thoroughly tested, including stress tests, error
scenarios, and multisite compatibility.
