Task and worker assignment model

Design and implement Task and Worker classes, then drive them to print the system's state. Tasks and workers are registered with unique IDs. A task starts pending, can be assigned once to a free worker, and is then assigned; a worker holds at most one task at a time. Completing a task marks it done, remembers who did it, and frees the worker for another task. Reject invalid transitions (assigning a busy worker, completing an unassigned task) with clear errors, and print a stable status listing.