[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/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)
+}