fix: support Python 3.14 event loops

[luketainton]

Summary

• Explicitly create and register the event loop used by WebexWebsocketClient.run().
• Use the running loop when dispatching received messages.
• Add a Python 3.14 regression test and test it in tox and GitHub Actions.

Validation

• python -m pytest -q on Python 3.14.7: 42 passed, 88.74% coverage.

Python 3.14 no longer creates an event loop implicitly for asyncio.get_event_loop(), which caused WebexBot.run() to fail on startup.

[luketainton]

Same as #90