feat(ipc): allow configuring job entrypoint shutdown grace period (#6512)

[piyushrajyadav]

Fixes #6512

Summary

When a worker process shuts down, _JobProc currently waits for the job entrypoint task for a hard-coded 15 seconds before cancelling it. Some applications need shutdown to terminate an active call immediately (e.g. entrypoint_shutdown_timeout=0.0) rather than allow voice playout or entrypoint tasks to drain for the full 15-second grace period.

This PR adds an entrypoint_shutdown_timeout: float = 15.0 parameter to ServerOptions and AgentServer, passing it down through ProcPool, ProcJobExecutor, ThreadJobExecutor, ProcStartArgs, ThreadStartArgs, to _JobProc.

Changes Made

• worker.py: Added entrypoint_shutdown_timeout to ServerOptions and AgentServer.__init__, passed down in from_server_options and run().
• proc_pool.py: Added entrypoint_shutdown_timeout to ProcPool.__init__, passed down to job executors.
• job_proc_executor.py: Passed entrypoint_shutdown_timeout through process startup args.
• job_thread_executor.py: Passed entrypoint_shutdown_timeout through thread startup args.
• job_proc_lazy_main.py: Replaced hardcoded timeout=15 in _JobProc._run_job_task() with self._entrypoint_shutdown_timeout.
• tests/test_entrypoint_shutdown_timeout.py: Added unit tests covering option propagation and fast entrypoint cancellation.

Test Plan

• Ran unit tests: python -m pytest tests/test_entrypoint_shutdown_timeout.py --unit (2 passed)
• Ran ruff check & ruff format

[CLAassistant]

All committers have signed the CLA.