For repositories with shallow mode enabled, before, Zed instantly loaded
diff changes which could be very large and CPU-demanding:


https://github.com/user-attachments/assets/5577730a-efef-424f-b749-501394a8b51f

Now, we show the following state instead of loading:

<img width="1728" height="1084" alt="after"
src="https://github.com/user-attachments/assets/03cc47fe-7074-4e8b-ba12-2fefa101377d"
/>

(the button allows to move on and do the load nonetheless)


Release Notes:

- Fixed shallow diffs causing a lot of computations

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>