simplify: dedupe boilerplate and remove dead code across all layers

lib/state/app/modules/chat_list/bloc/chat_list_bloc.dart

@@ -3,10 +3,8 @@ import 'dart:developer';
 
 import 'package:flutter_app_badge/flutter_app_badge.dart';
 
-import '../../../../../api/errors/error_mapper.dart';
 import '../../../../../api/marianumcloud/talk/chat/get_chat_response.dart';
 import '../../../../../api/marianumcloud/talk/room/get_room_response.dart';
-import '../../../infrastructure/loadable_state/loading_error.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc.dart';
 import '../../../infrastructure/utility_widgets/loadable_hydrated_bloc/loadable_hydrated_bloc_event.dart';
 import '../repository/chat_list_repository.dart';
@@ -87,17 +85,7 @@ class ChatListBloc
     } catch (e) {
       capturedError = e;
     }
-    if (capturedError != null) {
-      add(
-        Error(
-          LoadingError(
-            message: errorToUserMessage(capturedError),
-            technicalDetails: errorToTechnicalDetails(capturedError),
-            allowRetry: errorAllowsRetry(capturedError),
-          ),
-        ),
-      );
-    }
+    if (capturedError != null) addLoadingError(capturedError!);
   }
 
   /// Creates (or resolves) a 1:1 chat and returns its room token, or null in