fix: eager load Position and TelegramUser to eliminate N+1 queries in get_users_for_notifications

[chuks68]

This PR resolves the N+1 query issue in UserDBConnector.get_users_for_notifications by eager loading the related Position and TelegramUser entities using SQLAlchemy's joinedload.

• Changes:
  • Configured positions and telegram_user relationships on the User model.
  • Updated the query in get_users_for_notifications to apply .options(joinedload(User.positions), joinedload(User.telegram_user)).
  • Re-mapped query outputs to return the expected (contract_address, telegram_id) tuple type to preserve the existing signature and behavior.
• Impact:
  • Reduces database load from O(N) queries to a single joined query when fetching users for notification dispatches.