simplify: dedupe boilerplate and remove dead code across all layers

lib/api/marianumcloud/talk/vote_poll/vote_poll.dart

@@ -3,6 +3,7 @@ import 'dart:convert';
 import 'package:http/http.dart' as http;
 
 import '../../../api_params.dart';
+import '../../nextcloud_ocs.dart';
 import '../get_poll/get_poll_state_response.dart';
 import '../talk_api.dart';
 import 'vote_poll_params.dart';
@@ -22,12 +23,8 @@ class VotePoll extends TalkApi<GetPollStateResponse> {
        );
 
   @override
-  GetPollStateResponse assemble(String raw) {
-    final decoded = jsonDecode(raw) as Map<String, dynamic>;
-    return GetPollStateResponse.fromJson(
-      decoded['ocs'] as Map<String, dynamic>,
-    );
-  }
+  GetPollStateResponse assemble(String raw) =>
+      GetPollStateResponse.fromJson(NextcloudOcs.decode(raw));
 
   @override
   Future<http.Response>? request(