simplified code across the app and consolidated duplicated helpers

lib/api/marianumcloud/cloud_users/cloud_users_actions.dart

@@ -1,4 +1,3 @@
-import 'dart:convert';
 import 'dart:developer';
 import 'dart:typed_data';
 
@@ -96,9 +95,8 @@ class GetUserInfo {
       uri,
     );
     try {
-      final root = jsonDecode(response.body) as Map<String, dynamic>;
       final data =
-          (root['ocs'] as Map<String, dynamic>)['data'] as Map<String, dynamic>;
+          NextcloudOcs.decode(response.body)['data'] as Map<String, dynamic>;
       return CloudUserInfo(
         userId: data['id'] as String,
         displayName: (data['displayname'] as String?) ?? '',