PYTHON-5975 Fix missing await calls in async test suite

[blink1073]

PYTHON-5975

Changes in this PR

• Replaced ResetPoolThread in test_reset_during_update_pool with the existing ConcurrentRunner test helper, since the raw threading.Thread called its async _run() without awaiting it (and a Thread.run() has no event loop to run it in anyway).
• Fixed InsertEventListener.succeeded() so it actually runs the configureFailPoint admin command instead of discarding an unawaited coroutine. succeeded() is invoked synchronously by the shared command-monitoring dispatch code and can't become async, so the async path now schedules the command via create_task.

Test Plan

• just synchro, just lint, and mypy --config-file mypy_test.ini test all pass with no new errors.
• test/test_client.py::TestClient::test_reset_during_update_pool passes against a local standalone server; confirmed it also passes with the require_sync skip temporarily removed, proving the ConcurrentRunner-based fix genuinely works under async execution.
• Full test/test_client.py and test/test_retryable_writes.py suites (sync and async) pass locally; replica-set-gated tests skip against the standalone server available here. InsertEventListener's sync-mode behavior is unchanged from before this PR, so no regression risk there.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)? Not needed — test-only fix, no user-facing behavior change.
• Is there test coverage?
• Is any followup work tracked in a JIRA ticket? If so, add link(s). None needed.

Checklist for Reviewer

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Is all relevant documentation (README or docstring) updated?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!