- **Recurring Events**: Advanced modification scopes for recurring events (single instance, all instances, or future instances only)

The `RecurringEventHelpers` class provides specialized functionality for managing recurring calendar events:

- **Event Type Detection:** Identifies whether an event is recurring or single-occurrence

- **Instance ID Formatting:** Generates proper Google Calendar instance IDs for single occurrence modifications

- **Series Splitting:** Implements the complex logic for splitting recurring series with UNTIL clauses

- **Duration Preservation:** Maintains event duration across timezone changes and modifications

- **RRULE Processing:** Handles recurrence rule updates while preserving EXDATE and RDATE patterns

The `UpdateEventHandler` has been enhanced to support three modification scopes:

- **Single Instance:** Modifies one occurrence using instance IDs

- **All Instances:** Updates the master event (default behavior for backward compatibility)

- **Future Instances:** Splits the series and creates a new recurring event from a specified date forward

This architecture maintains full backward compatibility while providing advanced recurring event management capabilities.