[Feature request] 希望能够增加快速统计一个时序内部的数据数量的功能。

### Search before asking

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

### Motivation

想快速统计表里有多少条数据，用来展示给最终用户查看，或者用来给用户根据数量计费

### Solution

如果内部有这个信息的话，希望能提供接口进行查询

### Alternatives

_No response_

### Are you willing to submit a PR?

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

No files, tests, or entry points are named. Start by locating IoTDB's public query or API surface and checking whether existing time-series metadata can provide a data count; done means a clearly specified interface can return the count for billing or user display, with behavior and scope agreed.

Written by the indexing model from the issue text.