Use Xet high performance mode for Transformers v5 (#35098)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/model_executor/model_loader/weight_utils.py

@@ -80,6 +80,17 @@ def enable_hf_transfer():
             pass
 
 
+def enable_xet_high_performance():
+    """automatically activates xet high performance mode"""
+    if "HF_XET_HIGH_PERFORMANCE" not in os.environ:
+        huggingface_hub.constants.HF_XET_HIGH_PERFORMANCE = True
+
+
+if hasattr(huggingface_hub.constants, "HF_XET_HIGH_PERFORMANCE"):
+    # Transformers v5
+    enable_xet_high_performance()
+else:
+    # Transformers v4
     enable_hf_transfer()