[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/examples/thrust_flexible_device_system/example.cpp

@@ -0,0 +1,50 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2023-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <thrust/device_vector.h>
+#include <thrust/reduce.h>
+
+#include <iostream>
+
+int main()
+{
+  constexpr std::size_t N = 1000;
+  thrust::device_vector<int> data(N, 1);
+
+  const auto result = thrust::reduce(data.cbegin(), data.cend());
+
+  std::cout << "Sum: " << result << '\n';
+
+  if (result != N)
+  {
+    std::cerr << "Error: Expected sum of " << N << ", but got " << result << '\n';
+    return 1;
+  }
+
+  std::cout << "Detected device system: ";
+#if THRUST_DEVICE_SYSTEM == THRUST_DEVICE_SYSTEM_CUDA
+  std::cout << "CUDA" << '\n';
+#elif THRUST_DEVICE_SYSTEM == THRUST_DEVICE_SYSTEM_TBB
+  std::cout << "TBB" << '\n';
+#elif THRUST_DEVICE_SYSTEM == THRUST_DEVICE_SYSTEM_OMP
+  std::cout << "OMP" << '\n';
+#elif THRUST_DEVICE_SYSTEM == THRUST_DEVICE_SYSTEM_CPP
+  std::cout << "CPP" << '\n';
+#endif
+
+  return 0;
+}