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

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

The pack-objects command has been updated to support 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