[CCCL] Add missing CCCL components: c2h, nvbench_helper, cmake, cudax, AGENTS.md

Added 863 files from NVIDIA/cccl sparse checkout:
- c2h/ (27 files): Catch2 test helpers — generators, validators, runner
- nvbench_helper/ (10 files): Benchmark harness utilities
- cmake/ (29 files): CMake presets and build helpers
- cudax/ (794 files): Experimental CUDA extensions
- AGENTS.md: NVIDIA's official AI agent instructions for CCCL
- CMakePresets.json: Standardized build configurations
- cccl-version.json: Version tracking

Also added CCCL_ASSET_MAP.md mapping all 4295 CCCL files to
competition value and PRD items.

cccl_upstream now covers 100% of competition-critical assets:
- 27 tuning headers (SM80/90/100 benchmark data)
- 32 dispatch headers (algorithm implementations)
- 60 Thrust examples (correctness verification)
- 217 CUB Catch2 tests (regression matrix)
- 153 CUB benchmarks (parameter space search)
- 18 CUB examples (API verification)
- 27 test helpers + benchmark harness
- 794 cudax experimental extensions

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();
+}