Handle modern events without ding IDs - #556

Summary

Modern FCM events can omit event["ding"]["id"]. The current parser raises KeyError, and repeated notification errors can stop delivery.

Fix

• Use event["eventito"]["timestamp"] as a stable fallback only when ding.id is absent.
• Ignore an event when neither stable identifier exists.
• Preserve existing duplicate/update semantics.

Tests

• Missing ding.id fallback.
• Duplicate/update behavior.
• Malformed events without either ID.

Scope and coordination

PR #553 owns cocoa_doorbell_v5 and the other new device model/capability mappings. This PR deliberately contains no device-kind, model, or capability changes and complements #553.

Closed PR #518 identified the payload and confirmed that riid is not unique. The Home Assistant discussion at https://github.com/orgs/home-assistant/discussions/2520 provides downstream context; this parser-only PR alone does not create entities.

Validation

python -m compileall -q ring_doorbell tests and git diff --check pass. Full local pytest/Ruff validation was unavailable because package-index TLS prevented dependency installation.