Restore IMAGE_EXTENSIONS in the text_to_image FID helper

[David-Wu1119]

Summary

text_to_image/tools/fid/fid_score.py globs an image directory using IMAGE_EXTENSIONS, but that name is never defined anywhere in the module:

else:
    path = pathlib.Path(path)
    files = sorted(
        [file for ext in IMAGE_EXTENSIONS for file in path.glob(
            "*.{}".format(ext))]
    )

So compute_statistics_of_path() — and through it the public calculate_fid_given_paths() — raises NameError: name 'IMAGE_EXTENSIONS' is not defined for any path that is not a .npz. ruff --select F821 flags it.

The constant is defined in the upstream pytorch-fid this file is derived from; it looks like it was dropped when the module was vendored. This adds it back with the same extension set.

Reachability, honestly

The repo's own accuracy path is unaffected: tools/accuracy_coco.py passes statistics_path, which takes the .npz branch. The broken branch is reached when calculate_fid_given_paths is given a directory of images — the standard pytorch-fid usage and a documented shape for this public helper, but not something the benchmark's own scripts do.

So this is a latent defect rather than something breaking a submission run today. Filing it because a public function raising NameError on a supported input is worth having fixed, not because anything is currently failing.

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