Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Closes #57092

Before:

<img width="3400" height="2210" alt="image"
src="https://github.com/user-attachments/assets/0056817e-4826-46c1-85d4-e84c9c8d80f1"
/>

After:

<img width="1700" height="1105" alt="image"
src="https://github.com/user-attachments/assets/0ed86e42-20d7-41a0-90b6-102dfb57cc33"
/>

Release Notes:

- Add notebook cell stop button.

---------

Co-authored-by: Martin Ye <martin@zed.dev>
Co-authored-by: Yara <git@yara.blue>