并行消费问题

开启并行消费，例如窗口大小5，批量大小默认10，消费一段时间后，如果主题生产者停止发送消息后，消费会立刻停止，一直卡住不消费，直到如果后续生产继续那么消费也会开始消费，可以进行反复操作复现该问题。

Start by reproducing the issue with parallel consumption window 5 and the default batch size of 10, then inspect the consumer path that runs after the producer stops sending messages. The work is done when consumption does not remain stuck during producer inactivity and a regression test covers stopping and resuming production.

由索引模型根据 Issue 内容生成。