Rebatch arrow iterables before formatted iterable
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_7553). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. @lhoestq Our CI found an issue with this changeset causing a regression with shuffling iterable datasets 
<img width="884" alt="Screenshot 2025-05-07 at 9 16 52 AM" src="https://github.com/user-attachments/assets/bf7d9c7e-cc14-47da-8da6-d1a345992d7c" />

close https://github.com/huggingface/datasets/issues/7538 and https://github.com/huggingface/datasets/issues/7475