simplify: dedupe boilerplate and remove dead code across all layers

lib/api/marianumconnect/queries/timetable_get_classes/timetable_get_classes.dart

@@ -4,13 +4,11 @@ import 'timetable_get_classes_response.dart';
 class TimetableGetClasses extends MarianumConnectQuery {
   TimetableGetClasses({super.dio});
 
-  Future<TimetableGetClassesResponse> run() => guard(() async {
-    final response = await dio.get<List<dynamic>>(
-      endpoint('timetable/elements/classes'),
-    );
-    final list = response.data!
-        .map((e) => McTimetableClass.fromJson(e as Map<String, dynamic>))
-        .toList();
-    return TimetableGetClassesResponse(result: list);
-  });
+  Future<TimetableGetClassesResponse> run() async =>
+      TimetableGetClassesResponse(
+        result: await getList(
+          'timetable/elements/classes',
+          McTimetableClass.fromJson,
+        ),
+      );
 }