Implement WorkerPool for efficient worker management in parallel processing

[ahmadileham]

• Introduced a WorkerPool class to manage and reuse workers, reducing overhead from frequent creation and termination.
• Refactored _spawnWorker to leverage the WorkerPool, enhancing performance and scalability.
• Updated the Parallel constructor to initialize the WorkerPool with a configurable maxWorkers setting.
• Simplified error handling and added more descriptive error messages for easier debugging.
• Reduced redundant logic across worker management, making the codebase cleaner and more maintainable.