Add vLLM v0.18.1 source tree with KV transfer abort fix

third_party/vllm/ now tracked in git for direct patch management.
Based on vLLM v0.18.1 release with one patch applied:

  vllm/v1/core/sched/scheduler.py:
    Replace fatal assert with graceful skip when KV transfer callback
    arrives for an already-aborted request during PD disaggregated serving.

Future vLLM modifications should be made directly in third_party/vllm/
and committed normally. The patches/ directory is kept as documentation
of what changed from upstream.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

third_party/vllm/tests/quantization/utils.py

@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from vllm.model_executor.layers.quantization import get_quantization_config
+from vllm.platforms import current_platform
+
+
+def is_quant_method_supported(quant_method: str) -> bool:
+    # Currently, all quantization methods require Nvidia or AMD GPUs
+    if not (current_platform.is_cuda() or current_platform.is_rocm()):
+        return False
+
+    try:
+        current_platform.verify_quantization(quant_method)
+    except ValueError:
+        return False
+
+    capability = current_platform.get_device_capability()
+    assert capability is not None
+
+    min_capability = get_quantization_config(quant_method).get_min_capability()
+
+    return capability.to_int() >= min_capability