feat: enhance calendar ICS generation with event type filtering

- Added support for filtering calendar events by type in the ICS generation API endpoint, allowing users to specify whether to include only duty shifts or all event types (duty, unavailable, vacation).
- Updated the `get_duties_for_user` function to accept an optional `event_types` parameter, enabling more flexible data retrieval based on user preferences.
- Enhanced unit tests to cover the new event type filtering functionality, ensuring correct behavior and reliability of the ICS generation process.

tests/test_handlers_group_duty_pin.py

@@ -70,15 +70,11 @@ async def test_update_group_pin_edits_message_and_schedules_next():
     context.application.job_queue.get_jobs_by_name = MagicMock(return_value=[])
     context.application.job_queue.run_once = MagicMock()
 
-    with patch.object(
-        mod, "_sync_get_message_id", return_value=1
-    ):
+    with patch.object(mod, "_sync_get_message_id", return_value=1):
         with patch.object(
             mod, "_get_duty_message_text_sync", return_value="Current duty"
         ):
-            with patch.object(
-                mod, "_get_next_shift_end_sync", return_value=None
-            ):
+            with patch.object(mod, "_get_next_shift_end_sync", return_value=None):
                 with patch.object(mod, "_schedule_next_update", AsyncMock()):
                     await mod.update_group_pin(context)
     context.bot.edit_message_text.assert_called_once_with(