[conftest] Also wrap snapshot_download for EROFS fallback (#47796)
* [conftest] also wrap snapshot_download for EROFS fallback
`kernels` calls both `api.hf_hub_download` and `api.snapshot_download`.
`HfApi.snapshot_download` uses a local import at call time:
`from ._snapshot_download import snapshot_download`
so patching `_snapshot_download.snapshot_download` is picked up correctly.
Wrapping the entire `snapshot_download` (rather than its inner
`hf_hub_download` calls) ensures the retry uses `cache_dir=tmp_dir`
everywhere — `_inner_hf_hub_download` passes `cache_dir` explicitly,
so all files and the returned snapshot path land in the tmp dir.
The OSError from a failed thread propagates through `future.result()`
and `hf_thread_map` as a plain OSError, which the wrapper catches.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
* another
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Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>