Move Microsoft calendar event deletions from api to sync pods

In case of Google you can still fetch deleted events from the API even though they disappear in your calendar. In case of Microsoft they disappear both from the API and calendar, so they cannot be fetched in sync pods and synced there, the only way we can now something got deleted is in the webhook notifications.

To do less work (especially when cancelling recurrences with overrides) that could be potentially done in the background instead of marking events as cancelled directly in the api, store the uids of deleted events in a table event_cancellations(id PARIMARY KEY, calendar_id INT, uid TEXT, created_at DATETIME) and then change sync_events to fetch those events from database there, clone them, set as cancelled and then delete records from event_cancellations

Start with inbox/events/microsoft/events_provider.py at the linked sync_events entry point, then trace the Microsoft deletion handling in the API path. Implement the event_cancellations persistence and deferred cancellation flow described in the issue, including cleanup after sync, and verify that deleted events are represented as cancelled without doing the work directly in the API.