Handle merge commits more elegantly

[bestdan]

Given the following situation:

• I'm working on a feature branch that falls behind main
• I pull merge main into my feature branch
• I push my files back up

tsu collate runs on all the changes files in the merge commit, not just the files that have changed in my feature branch. This results in an unnecessarily long tsu collate check.

Please review the code that determines getAllChangedFiles and think carefully about a solution that would improve efficiency while not losing fidelity or resilience.