Handle FCM events without ding IDs - #540

Summary

• Handle Ring FCM payloads that omit event.ding.id.
• Derive a deterministic fallback event ID from created_at.
• Preserve event delivery and duplicate-update detection.
• Prevent repeated KeyError callback failures from shutting down real-time events for all devices.
• Add regression coverage for repeated ID-less motion notifications.

Fixes #537

Testing

• uv run pre-commit run --files ring_doorbell/listen/eventlistener.py tests/test_listen.py --verbose
• uv run pytest tests/ --force-enable-socket --cov=ring_doorbell --cov-report=xml --cov-report=term-missing --import-mode importlib
• Built and tested in Home Assistant Container.
• Confirmed motion event entities update for multiple Ring cameras and doorbells.