[Bug] When batching is enabled even when no data is being streamed CPU usage remains high post streaming to 1.5k topics

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Read release policy

- [X] I understand that unsupported versions don't get bug fixes. I will attempt to reproduce the issue on a supported version of Pulsar client and Pulsar broker.

### Version

2.10.6

### Minimal reproduce step

With batching enabled stream data to 1500 topics, then stop streaming and monitor the CPU usage
When batching is enabled


When batching is disabled


### What did you expect to see?

CPU utilization should come down to 2-3% when data is not being streamed

### What did you see instead?

CPU utilization is high even when data is not being streamed

### Anything else?

This is seen only when batching is enabled. When batching is disabled it works as expected.

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start with the minimal reproduction described in the issue on Pulsar 2.10.6: stream data to 1,500 topics with batching enabled, stop the stream, and compare CPU usage with batching disabled. No source files or tests are named; done means identifying and fixing the batching-related post-stream CPU activity so utilization falls to the expected 2–3%.

Written by the indexing model from the issue text.