[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/cudax/test/stf/dot/basic.cu

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDASTF in CUDA C++ Core Libraries,
+// under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+// SPDX-FileCopyrightText: Copyright (c) 2022-2024 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+/**
+ * @file
+ * @brief This test makes sure we can generate a dot file
+ */
+
+#include <cuda/experimental/stf.cuh>
+
+using namespace cuda::experimental::stf;
+
+int main()
+{
+// TODO (miscco): Make it work for windows
+#if !_CCCL_COMPILER(MSVC)
+  // Generate a random filename
+  int r = rand();
+
+  char filename[64];
+  snprintf(filename, 64, "output_%d.dot", r);
+  // fprintf(stderr, "filename %s\n", filename);
+  setenv("CUDASTF_DOT_FILE", filename, 1);
+
+  stream_ctx ctx;
+
+  auto lA = ctx.logical_data(shape_of<slice<char>>(64));
+  ctx.task(lA.write())->*[](cudaStream_t, auto) {};
+  ctx.task(lA.rw())->*[](cudaStream_t, auto) {};
+  ctx.finalize();
+
+  // Call this explicitly for the purpose of the test
+  reserved::dot::instance().finish();
+
+  // Make sure the file exists, and erase it
+  // fprintf(stderr, "ERASE. ...\n");
+  EXPECT(access(filename, F_OK) != -1);
+
+  EXPECT(unlink(filename) == 0);
+#endif // !_CCCL_COMPILER(MSVC)
+}