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/requirements/rocm-build.txt

@@ -0,0 +1,16 @@
+# Common dependencies
+-r common.txt
+
+--extra-index-url https://download.pytorch.org/whl/rocm7.1
+torch==2.10.0
+torchvision==0.25.0
+torchaudio==2.10.0
+triton==3.6.0
+cmake>=3.26.1,<4
+packaging>=24.2
+setuptools>=77.0.3,<80.0.0
+setuptools-scm>=8
+wheel
+jinja2>=3.1.6
+amdsmi==7.0.2
+timm>=1.0.17