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/examples/online_serving/structured_outputs/pyproject.toml

@@ -0,0 +1,8 @@
+[project]
+name = "examples-online-structured-outputs"
+requires-python = ">=3.10, <3.14"
+dependencies = ["openai==1.78.1", "pydantic==2.11.4"]
+version = "0.0.0"
+
+[project.scripts]
+structured-outputs = "structured_outputs:main"