Update gix-blame to imara-diff 0.2

[cruessler]

This is a quick conversion of gix-blame to use imara-diff 0.2 through gix-diff’s new blob-experimental feature. I haven’t run any benchmarks yet, just wanted to open the PR, so you can have a look yourself! The update made one test that previously was marked should_panic pass, so that’s already promising. :-)

[Byron]

This looks very promising indeed! Some complexity now moved to imara-diff.

Let's see those performance comparisons as well :).
Until we are more sure how this works, you could put this change behind a feature flag as well, supporting both implementations side-by-side. Alternatively, this can stay open until we know what to do with V2. And… once it's clear that it is not slower, I guess it can just be adopted, provided all existing unified diff tests can be ported which will be quite an undertaking I suppose.

[cruessler]

I added a feature flag, blob-experimental, to gix-blame. This should hopefully also make the full diff easier to read as it now mostly contains additions and very few changes.

I decided to re-use the comment to blob-experimental that I copied from gix-diff. Feel free to re-phrase, though.

I’ll mark this PR as ready even though CI hasn’t completed yet (so I can turn off my computer :-)). If anything comes up, I’ll address it, but apart from that, I hope it is finished.

The only thing that’s missing is proably a line such as the following one in justfile:

cargo nextest run -p gix-blame --features blob-experimental --no-fail-fast