Add ability to revert hunk

[kjughx]

This PR adds the ability to revert individual hunks from the commit_view.

In order to do this I had to expand the Hunk type slightly, so that it can be just by itself with the corresponding Diff it belongs to. Namely I added two new fields:

1. file, the name of the file from the where the hunk applies
2. lines, this was already kind of part of the type except not in the documentation.

With these changes, the generate_patch can work without being passed an item, which doesn't exist in the context of a standalone hunk. It is now also able to parse the lines directly on Hunk, whether it is a SelectedHunk or not. The from and to parameters now represents the relative lines in the hunk buffer.

With these changes; reverting a hunk is now only a matter of doing a git apply --reverse with a patch from generate_patch.

[CKolkey]

this is really great! Some minor tweaks then lets get this merged.

[kjughx]

I'm not sure about these failing tests, if they're my fault or not, because I cannot figure out how to run them locally.

[CKolkey]

I don't think it's your fault, and I'll add some instructions on how to do that.

(you'll need a ruby runtime (3.3.6) and run bundle && CI=1 bundle exec rspec --format Fuubar)

[kjughx]

I tried that but seems my version (3.2.3) of ruby is not compatible.

[CKolkey]

No worries - this looks good as is. Thanks for taking the time!