Closes #51573
Closes #52852 * I believe, looking for verification of that.

A very similar issue was belived to be fixed with #51642 , however it
seems like there is still some edge cases that were causing crashes.
These issues appeared to me to be caused by the dedup method failing to
catch sub-ranges (created by entering SelectMode after the search) as
duplicates.

two new tests that isolate the case in 51573 and 52852 respectively.

fixed vid:


https://github.com/user-attachments/assets/f62d5210-6cb3-4bdf-a061-efc265eb2804



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



Release Notes:

- helix: Fix search selection range deduplication logic