Add delete_event functionality with series deletion option and tests

[iancanderson]

This pull request introduces the ability to delete either a single occurrence or all future occurrences of a recurring event in the calendar management system. It includes updates to the delete_event method, a new async function for deleting events, and corresponding tests.

[Omar-V2]

Hey, thank you so much for your contribution, really appreciate it! I've left a couple comments below:

• Could you also update the integration tests in tests/test_calendar_manage_integration.py to test the new delete event functionality?
• Could you add pytest-asyncio to the dev dependencies? uv add --dev pytest-asyncio
• I briefly tried out the delete event functionality and it didn't work entirely as intended (see this chat for reference)
• I tried asking it to delete a specific event in the series and it deleted the wrong one, after I tried deleting a different event in the series and it thought it had deleted it but it actually didn't.
• This may possibly be a bug in the original delete_event function that I wrote, if that's the case let me know and I can fix, but some new integration tests should help identify the issue.