better loading indicators for timetables, talk and files

lib/state/app/modules/chatList/dataProvider/chat_list_data_provider.dart

@@ -1,20 +1,26 @@
-import 'dart:async';
-
 import '../../../../../api/marianumcloud/talk/room/getRoomCache.dart';
 import '../../../../../api/marianumcloud/talk/room/getRoomResponse.dart';
 import '../../../../../api/marianumcloud/talk/createRoom/createRoom.dart';
 import '../../../../../api/marianumcloud/talk/createRoom/createRoomParams.dart';
 
 class ChatListDataProvider {
-  Future<GetRoomResponse> getRooms({bool renew = false}) {
-    final completer = Completer<GetRoomResponse>();
-    GetRoomCache(
+  Future<GetRoomResponse> getRooms({
+    void Function(Object)? onError,
+    bool renew = false,
+  }) async {
+    GetRoomResponse? latest;
+    Object? capturedError;
+    final cache = GetRoomCache(
       renew: renew,
-      onUpdate: (data) {
-        if (!completer.isCompleted) completer.complete(data);
+      onUpdate: (data) => latest = data,
+      onError: (e) {
+        capturedError = e;
+        onError?.call(e);
       },
     );
-    return completer.future;
+    await cache.ready;
+    if (latest != null) return latest!;
+    throw capturedError ?? Exception('No data and no error from getRooms');
   }
 
   Future<void> createDirectRoom(String invite) =>