simplify: dedupe boilerplate and remove dead code across all layers

lib/api/marianumconnect/queries/timetable_get_schoolyear/timetable_get_schoolyear.dart

@@ -4,10 +4,6 @@ import 'timetable_get_schoolyear_response.dart';
 class TimetableGetSchoolyear extends MarianumConnectQuery {
   TimetableGetSchoolyear({super.dio});
 
-  Future<TimetableGetSchoolyearResponse> run() => guard(() async {
-    final response = await dio.get<Map<String, dynamic>>(
-      endpoint('timetable/schoolyear'),
-    );
-    return TimetableGetSchoolyearResponse.fromJson(response.data!);
-  });
+  Future<TimetableGetSchoolyearResponse> run() =>
+      getObject('timetable/schoolyear', TimetableGetSchoolyearResponse.fromJson);
 }