feat: enhance Google Calendar integration and optimize notifications

Слиты opensource-effective-dev запросил слияние feature/remove-lonely-bookings в develop

Created by: Radch-enko

  • Implemented event deletion when all participants decline via deleteEvent method.
  • Refactored listEvents to modularize request building and processing.
  • Added buildEventsRequest, processEvents, and utility functions for better maintainability.
  • Reduced notification deduplication TTL to 5 seconds for faster processing.