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/csrc/quantization/machete/machete_interleaving_utils.cuh

@@ -0,0 +1,35 @@
+#pragma once
+
+#include "cutlass/cutlass.h"
+#include "cute/layout.hpp"
+
+namespace machete {
+
+using namespace cute;
+
+// get an interleaved block layout where each element consecutive element has a
+// stride of bit_stride and the block width is blk_bit_width,
+// examples:
+//  size_bits<T> = 8, bit_stride = 8,  blk_bit_width = 32 -> 4:1
+//  size_bits<T> = 8, bit_stride = 16, blk_bit_width = 32 -> (2, 2):(2, 1)
+//  size_bits<T> = 4, bit_stride = 8,  blk_bit_width = 32 -> (4, 2):(2, 1)
+//  size_bits<T> = 4, bit_stride = 16, blk_bit_width = 32 -> (2, 4):(4, 1)
+template <typename T, int bit_stride, int blk_bit_width>
+CUTE_HOST_DEVICE static constexpr auto get_interleaved_blk_layout() {
+  static_assert(blk_bit_width % bit_stride == 0);
+  static_assert(bit_stride % cute::sizeof_bits_v<T> == 0);
+
+  constexpr auto elems_per_blk = blk_bit_width / cute::sizeof_bits_v<T>;
+
+  if constexpr (cute::sizeof_bits_v<T> == bit_stride) {
+    // identity layout
+    return Layout<Shape<Int<elems_per_blk>>>{};
+  } else {
+    constexpr auto elems_per_stride = bit_stride / cute::sizeof_bits_v<T>;
+    constexpr auto num_strides = elems_per_blk / elems_per_stride;
+    return Layout<Shape<Int<num_strides>, Int<elems_per_stride>>,
+                  Stride<Int<elems_per_stride>, Int<1>>>{};
+  }
+}
+
+};  // namespace machete