simplify: dedupe boilerplate and remove dead code across all layers

lib/api/marianumconnect/queries/timetable_get_week/timetable_get_week.dart

@@ -7,14 +7,9 @@ class TimetableGetWeek extends MarianumConnectQuery {
   Future<TimetableGetWeekResponse> run({
     required DateTime from,
     required DateTime until,
-  }) => guard(() async {
-    final response = await dio.get<Map<String, dynamic>>(
-      endpoint('timetable/me'),
-      queryParameters: {'from': _format(from), 'until': _format(until)},
-    );
-    return TimetableGetWeekResponse.fromJson(response.data!);
-  });
-
-  String _format(DateTime d) =>
-      '${d.year.toString().padLeft(4, '0')}-${d.month.toString().padLeft(2, '0')}-${d.day.toString().padLeft(2, '0')}';
+  }) => getObject(
+    'timetable/me',
+    TimetableGetWeekResponse.fromJson,
+    queryParameters: {'from': isoDate(from), 'until': isoDate(until)},
+  );
 }