Retry schedule updates on conflict token mismatch

[ningmao-hlyz]

What changed

• Pass the schedule describe response conflict token into update schedule requests.
• Retry the describe/update loop when the server reports a mismatched conflict token.
• Add a unit test covering the retry path and conflict token propagation.

Fixes #1367

Checks

• uv run pytest tests/test_client.py::test_schedule_update_retries_conflict_token
• uv run ruff check --select I temporalio/client/_impl.py tests/test_client.py
• uv run ruff format --check temporalio/client/_impl.py tests/test_client.py
• uv run pyright temporalio/client/_impl.py tests/test_client.py
• git diff --check