Queue delay not working as expected

[mdktdys]

For some reason, adding a function to the queue causes the previous one to end. Am I doing something wrong or is this intended? How can I get the expected result?

import 'dart:async';
import 'dart:developer';

import 'package:queue/src/dart_queue_base.dart';

void main() async {

  final Queue queue = Queue(delay: Duration(seconds: 6));

  Future<void> wait(String a) async {
    await queue.add(() => Future.delayed(Duration(milliseconds: 100)));
    log('$a ${DateTime.now()}');
  };

  wait('a');
  wait('b');
  await Future.delayed(Duration(milliseconds: 100));
  wait('c');


  await Future.delayed(Duration(seconds: 10));
}

result:
[log] a 2025-03-06 16:12:24.307348
[log] b 2025-03-06 16:12:24.412779
[log] c 2025-03-06 16:12:30.432560

excepted:
[log] a 2025-03-06 16:12:24.307348
[log] b 2025-03-06 16:12:30.332560
[log] c 2025-03-06 16:12:36.432560