Add download bandwidth limit option to kaggle datasets download

## Feature request: Add bandwidth limiting for downloads

### Problem
The Kaggle CLI can download very large datasets, but there is currently no way to limit download speed.

For example:
```bash
kaggle datasets download -d username/dataset
```

### Proposed solution
Add an option similar to tools like aria2/curl:

```bash
kaggle datasets download \
-d owner/dataset \
--max-download-rate 350K
```

Start at the implementation of the `kaggle datasets download` command and trace how it handles dataset transfers. Check how command-line options are defined and how download behavior is tested, then add the proposed `--max-download-rate` behavior so the example command can constrain bandwidth and existing downloads remain unaffected.

Written by the indexing model from the issue text.