Add timer sensor and timer actions for Webasto devices

[MTrab]

Summary

• add timer support to Home Assistant integration based on pywebasto timer API
• add a new diagnostic sensor for each device with state = next enabled timer and attributes containing all known simple timers
• add three new services for timer lifecycle management:
  • webastoconnect.create_timer
  • webastoconnect.update_timer
  • webastoconnect.delete_timer
• register/unregister services with config entry lifecycle
• add service metadata in services.yaml
• add/adjust tests for timer sensor logic, timer service logic, and setup/unload service lifecycle behavior

Configuration

• manifest.json requirement is set to pywebasto branch feature/timer-implementation-update for this test cycle

Test strategy

• ruff check custom_components/webastoconnect tests
• pytest -q

Test result

• lint passes
• all tests pass (36 passed)

Known limitations

• timer actions target simple timers only (matching current pywebasto scope)