Merge branch 'tb/pack-path-walk-bitmap-delta-islands' into jch

Merge branch 'tb/pack-path-walk-bitmap-delta-islands' into jch

The pack-objects command now supports using reachability bitmaps and
delta-islands concurrently with the `--path-walk` option, allowing
faster packaging by falling back to path-walk when bitmaps cannot
fully satisfy the request.

* tb/pack-path-walk-bitmap-delta-islands:
  pack-objects: support `--delta-islands` with `--path-walk`
  pack-objects: extract `record_tree_depth()` helper
  pack-objects: support reachability bitmaps with `--path-walk`
  t/perf: drop p5311's lookup-table permutation