[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/c2h/include/c2h/utility.h

@@ -0,0 +1,36 @@
+// SPDX-FileCopyrightText: Copyright (c) 2011-2023, NVIDIA CORPORATION. All rights reserved.
+// SPDX-License-Identifier: BSD-3
+
+#pragma once
+
+#include <cstdlib>
+#include <cstring>
+#include <string>
+#include <typeinfo>
+#ifdef __GNUC__
+#  include <cxxabi.h>
+#endif // __GNUC__
+
+namespace c2h
+{
+// TODO(bgruber): duplicated version of thrust/testing/unittest/system.h
+inline std::string demangle(const char* name)
+{
+#if __GNUC__ && !_NVHPC_CUDA
+  int status     = 0;
+  char* realname = abi::__cxa_demangle(name, nullptr, nullptr, &status);
+  std::string result(realname);
+  std::free(realname);
+  return result;
+#else // __GNUC__ && !_NVHPC_CUDA
+  return name;
+#endif // __GNUC__ && !_NVHPC_CUDA
+}
+
+// TODO(bgruber): duplicated version of thrust/testing/unittest/util.h
+template <typename T>
+std::string type_name()
+{
+  return demangle(typeid(T).name());
+}
+} // namespace c2h