[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/sections_2.cu

@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 with sections
+ */
+
+#include <cuda/experimental/stf.cuh>
+
+using namespace cuda::experimental::stf;
+
+int main()
+{
+// TODO (miscco): Make it work for windows
+#if !_CCCL_COMPILER(MSVC)
+  context ctx;
+  auto lA = ctx.token().set_symbol("A");
+  auto lB = ctx.token().set_symbol("B");
+  auto lC = ctx.token().set_symbol("C");
+
+  // Begin a top-level section named "foo"
+  auto s_foo = ctx.dot_section("foo");
+  for (size_t i = 0; i < 2; i++)
+  {
+    // Section named "bar" using RAII
+    auto s_bar = ctx.dot_section("bar");
+    ctx.task(lA.read(), lB.rw()).set_symbol("t1")->*[](cudaStream_t) {};
+    for (size_t j = 0; j < 2; j++)
+    {
+      // Section named "baz" using RAII
+      auto s_bar = ctx.dot_section("baz");
+      ctx.task(lA.read(), lC.rw()).set_symbol("t2")->*[](cudaStream_t) {};
+      ctx.task(lB.read(), lC.read(), lA.rw()).set_symbol("t3")->*[](cudaStream_t) {};
+      // Implicit end of section "baz"
+    }
+    // Implicit end of section "bar"
+  }
+  s_foo.end(); // Explicit end of section "foo"
+  ctx.finalize();
+#endif // !_CCCL_COMPILER(MSVC)
+}