status: ignore assume-unchanged submodule paths replaced by symlinks

[Copilot]

gix status was reporting an untracked entry when a tracked submodule path marked --assume-unchanged was replaced by a symlink. This diverged from Git, which keeps status clean for that case.

• What changed

  • Updated status classification in gix-dir to treat ASSUME_VALID index entries as “up-to-date” for index/disk kind resolution.
  • This prevents dirwalk from surfacing tracked assume-unchanged paths as untracked when their on-disk type differs (e.g., directory → symlink).

• Reproduction coverage added

  • Extended make_status_repos.sh with a focused fixture:
    • repo with a committed submodule
    • submodule marked --assume-unchanged
    • submodule path replaced by a symlink
  • Added a status test asserting no emitted status items for this scenario.

• Key implementation detail

  • Classification now gates on either UPTODATE or ASSUME_VALID:

entry.flags.intersects(
    gix_index::entry::Flags::UPTODATE | gix_index::entry::Flags::ASSUME_VALID
)

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