[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/section_movable.cu

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+// 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) 2022-2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+/**
+ * @file
+ * @brief Test if dot section guards are movable and if we can them as an optional value
+ */
+
+#include <cuda/experimental/stf.cuh>
+
+#include <optional>
+#include <vector>
+
+using namespace cuda::experimental::stf;
+
+int main()
+{
+  context ctx;
+
+  // Ensure the guard is movable
+  {
+    auto g  = ctx.dot_section("foo");
+    auto g2 = mv(g);
+  }
+
+  // Ensure the guard can be stored as an optional
+  ::std::vector<::std::optional<reserved::dot_section::guard>> nested_sections;
+
+  for (size_t depth = 0; depth < 3; depth++)
+  {
+    nested_sections.emplace_back(ctx.dot_section("foo"));
+  }
+
+  for (size_t depth = 0; depth < 3; depth++)
+  {
+    nested_sections.pop_back();
+  }
+
+  ctx.finalize();
+}