ci: cover xet as well (runtime error) (#47338)
* cover xet as well (runtime error)
* xet is process-wide and caches locations. the rety now simply disables it
* reviews
* log read-only cache fallback invocations for CI validation
Record every call retried through the read-only cache fallback and report
the count (with triggering repo/file ids) in the pytest terminal summary, so
CI logs show unambiguously whether the fallback path was exercised.
* extend read-only cache fallback to hf_hub_download + make event counter xdist-safe
- Wrap huggingface_hub.hf_hub_download (and re-bind already-imported consumers like
peft.config) so direct downloads that bypass transformers.cached_files also get the
read-only retry. Fixes PEFT adapter_config.json loads against a read-only CI cache.
- Record fallback events to a shared per-process directory instead of an in-memory list,
so pytest-xdist worker events are aggregated by the controller's terminal summary.
