Linear map checkpoints

[Panzerhandschuh]

Checkpoints in linear maps were displaying as 1-1, 1-2, 1-3, etc. in the split comparison UI so I changed it to display just the subsegment number.

Checks

• I have thoroughly tested all of the code I have modified/added/removed to ensure something else did not break
• I have followed semantic commit messages e.g. feat: Add foo, chore: Update bar, etc...
• My branch has a clear history of changes that can be easy to follow when being reviewed commit-by-commit
• My branch is functionally complete; the only changes to be done will be those potentially requested in code review
• All changes requested in review have been fixuped into my original commits.
• Fully tokenized all my strings (no hardcoded English strings!!) and supplied bulk JSON strings below