Fix submodule skip directory matching

[JamBalaya56562]

Summary

This fixes a false-positive sl status deletion report when a repository has a root submodule path whose basename also appears in a normal nested directory.

The physical working copy walker receives submodule paths as directories to skip. It was comparing those skip entries against the current directory entry basename, so a root submodule such as examples also caused tests/misc/ino2cpp/examples to be skipped. Tracked files under the skipped nested directory were then reported as deleted.

Changes

• Compare skip directories against the root-relative candidate_path instead of the entry basename.
• Add a walker unit test that skips root examples while still walking tests/misc/ino2cpp/examples.

Validation

• mise exec rust@nightly -- cmd /v:on /c "set CARGO_HOME=C:\c&& cargo fmt --check -p sapling-workingcopy"
• Attempted mise exec rust@nightly -- cmd /v:on /c "set CARGO_HOME=C:\c&& cargo test -p sapling-workingcopy --lib test_multiwalker_skip_dirs_are_repo_relative -- --exact", but the local Windows build stopped before running the test because openssl-sys could not find an OpenSSL/vcpkg installation.

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D110681347. (Because this pull request was imported automatically, there will not be any future comments.)