Follow-up to durable-workflow/server#4.

Summary

• send a poll_request_id on workflow task polls
• retry one timed-out workflow poll once with the same request id so the server can replay a cached leased task instead of dropping it
• keep the client test surface aligned with the dynamic request id field

Validation

• . .venv/bin/activate && python -m pytest tests/test_client.py -k "poll_workflow_task"