refactored chat data fetching to support separate cache and network callbacks

lib/state/app/modules/chat/data_provider/chat_data_provider.dart

@@ -2,26 +2,18 @@ import '../../../../../api/marianumcloud/talk/chat/get_chat_cache.dart';
 import '../../../../../api/marianumcloud/talk/chat/get_chat_response.dart';
 
 class ChatDataProvider {
-  Future<GetChatResponse> getChat({
+  Future<void> getChat({
     required String token,
-    void Function(GetChatResponse data)? onUpdate,
+    void Function(GetChatResponse data)? onCacheData,
+    void Function(GetChatResponse data)? onNetworkData,
     void Function(Object)? onError,
   }) async {
-    GetChatResponse? latest;
-    Object? capturedError;
     final cache = GetChatCache(
       chatToken: token,
-      onUpdate: (data) {
-        latest = data;
-        onUpdate?.call(data);
-      },
-      onError: (e) {
-        capturedError = e;
-        onError?.call(e);
-      },
+      onCacheData: onCacheData,
+      onNetworkData: onNetworkData,
+      onError: (e) => onError?.call(e),
     );
     await cache.ready;
-    if (latest != null) return latest!;
-    throw capturedError ?? Exception('No data and no error from getChat');
   }
 }