Add timeout-based straggler resubmission in ParallelExecutor

[okhat]

• Added new parameters timeout_seconds (default 120) and straggler_limit (default 3) to control when slow tasks are re-executed.
• Modified multi-thread execution to record the actual start time of tasks inside the worker thread, ensuring accurate timeout detection even when tasks are queued.
• Updated the executor loop to poll for completed futures and, if only a few tasks remain and any exceed the timeout, resubmit them exactly once.
• Ensured that once a task’s result is returned (from either the original or resubmitted copy), it is recorded and the overall execution terminates immediately without waiting for the slow original.
• Maintained all existing behaviors including thread-local overrides, error handling, progress bar updates, and signal (SIGINT) interruption handling.