improve hf_hub activation (#1438)

lm_eval/models/__init__.py

@@ -11,12 +11,11 @@ from . import neuron_optimum
 # TODO: implement __all__
 
 
-import os
-
 try:
-    # enabling faster model download
-    import hf_transfer
+    # enable hf hub transfer if available
+    import hf_transfer  # type: ignore # noqa
+    import huggingface_hub.constants  # type: ignore
 
-    os.environ["HF_HUB_ENABLE_HF_TRANSFER"] = "1"
+    huggingface_hub.constants.HF_HUB_ENABLE_HF_TRANSFER = True
 except ImportError:
     pass