Update local_calendar/todo to avoid blocking in the event loop

[allenporter]

Proposed change

Update local_calendar/todo to avoid blocking in the event loop. These methods may work with timezone libraries that may read from disk to ensure the calendar has necessarily timezone information built in.

This adds a lock just to be extra safe that there are not concurrent modifications happening to the calendar object. This may have been an existing risk, but is now more obvious with allowing a task to do the modification.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Detected blocking call to open inside the event loop by integration 'local_todo' #120576
• This PR is related to issue:
• Link to documentation pull request:

Checklist

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