Skip uninteresting commits for blame

[cruessler]

This PR is a PoC. It is a first attempt at implementing custom graph traversal for blame::file. This allows us to skip commits that we know don’t contain changes to the file being blamed. The PR is rough around the edges and contains a lot of TODOs and todo!()s.

A first round of tests showed a significant reduction in the number of commits traversed for gix blame STABILITY.md:

# before
Statistics {
    commits_traversed: 9261,
    commits_to_tree: 10710,
    trees_decoded: 10710,
    trees_diffed: 37,
    blobs_diffed: 36,
}

# after
Statistics {
    commits_traversed: 3657,
    commits_to_tree: 3749,
    trees_decoded: 3749,
    trees_diffed: 37,
    blobs_diffed: 36,
}

Also, profiling gix blame STABILITY.md on my machine revealed that the command took about 20 % less time to run.

[cruessler]

I think (and hope :-)) that this PR is now ready for the first round of reviews. There’s still two or three todo!() left, but I’ve addressed all of the TODOs as far as I can see and I’m really satisfied with the numbers so far as there seems to be a considerable speedup.

Also, the traversal is now much closer to what git does, and I hope that it most of the time is even identical unless there are differences in diffing results that can make traversals diverge. I haven’t found ways to validate this claim at a large scale, though, so I want to be cautious at this point.

gitoxide on  main [!?⇣] is 📦 v0.40.0 via 🦀 v1.84.0 took 5s
❯ hyperfine "$HOME/github/Byron/gitoxide/target/release/gix blame STABILITY.md" "$HOME/worktrees/gitoxide/branch-1/target/release/gix blame STABILITY.md"
Benchmark 1: /home/christoph/github/Byron/gitoxide/target/release/gix blame STABILITY.md
  Time (mean ± σ):     194.6 ms ±   2.3 ms    [User: 174.0 ms, System: 19.8 ms]
  Range (min … max):   190.8 ms … 198.5 ms    15 runs

Benchmark 2: /home/christoph/worktrees/gitoxide/branch-1/target/release/gix blame STABILITY.md
  Time (mean ± σ):      99.2 ms ±   1.5 ms    [User: 87.3 ms, System: 11.3 ms]
  Range (min … max):    97.1 ms … 104.1 ms    29 runs

Summary
  '/home/christoph/worktrees/gitoxide/branch-1/target/release/gix blame STABILITY.md' ran
    1.96 ± 0.04 times faster than '/home/christoph/github/Byron/gitoxide/target/release/gix blame STABILITY.md'