[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/thrust/testing/reduce_large.cu

@@ -0,0 +1,38 @@
+#include <thrust/reduce.h>
+
+#include <unittest/unittest.h>
+
+template <typename T, unsigned int N>
+void _TestReduceWithLargeTypes()
+{
+  size_t n = (64 * 1024) / sizeof(FixedVector<T, N>);
+
+  thrust::host_vector<FixedVector<T, N>> h_data(n);
+
+  for (size_t i = 0; i < h_data.size(); i++)
+  {
+    h_data[i] = FixedVector<T, N>(static_cast<T>(i));
+  }
+
+  thrust::device_vector<FixedVector<T, N>> d_data = h_data;
+
+  FixedVector<T, N> h_result = thrust::reduce(h_data.begin(), h_data.end(), FixedVector<T, N>(T{0}));
+  FixedVector<T, N> d_result = thrust::reduce(d_data.begin(), d_data.end(), FixedVector<T, N>(T{0}));
+
+  ASSERT_EQUAL_QUIET(h_result, d_result);
+}
+
+void TestReduceWithLargeTypes()
+{
+  _TestReduceWithLargeTypes<int, 4>();
+  _TestReduceWithLargeTypes<int, 8>();
+  _TestReduceWithLargeTypes<int, 16>();
+
+  // XXX these take too long to compile
+  //  _TestReduceWithLargeTypes<int,   32>();
+  //  _TestReduceWithLargeTypes<int,   64>();
+  //  _TestReduceWithLargeTypes<int,  128>();
+  //  _TestReduceWithLargeTypes<int,  256>();
+  //  _TestReduceWithLargeTypes<int,  512>();
+}
+DECLARE_UNITTEST(TestReduceWithLargeTypes);