persistence of unassigned changes that survives application restarts

[Byron]

Here is a video of the problem, watch for the flashing of the 'previous unassigned files' which really is just there for a couple for frames.

https://github.com/user-attachments/assets/98f5debc-9ec1-44d7-8c01-9561dafa16cb

How to reproduce

• open the UI on a project
• in the project, create a bunch of files with for num in $(seq 1000); do touch $num; done
• watch the UI show the untracked files
• close the UI
• run git clean -f to get rid of the file
• open the UI and see the previous set of unchanged files flash briefly
  • Note that there will be no flash if ~/Library/Caches/com.gitbutler.app.nightly was removed before.

[Byron]

CC @estib-vega .