Fix broken rustfmt in git graph code (#54730)

rustfmt is broken in this code. I believe it's too deep / complex in the
builder pattern. After factoring some bits out, it now auto formats.

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)
- [ ] Tests cover the new/changed behavior
- [X] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A
b034259591Joseph T. Lyons committed on 4/24/2026, 11:44:36 AM· committed by GitHubparent250e697
1 file changedLine totals unavailable