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.