[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/cufile/cufile_ref.cu

@@ -0,0 +1,69 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of CUDA Experimental 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) 2025 NVIDIA CORPORATION & AFFILIATES.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cuda/std/type_traits>
+#include <cuda/std/utility>
+
+#include <cuda/experimental/cufile.cuh>
+
+#include <cufile.h>
+#include <testing.cuh>
+
+#include "common.h"
+
+C2H_CCCLRT_TEST("cuFile cufile_ref", "[cufile][cufile]")
+{
+  constexpr auto filename = "cufile_ref_test_file";
+
+  // 1. Test public cufile_ref types and properties.
+  STATIC_REQUIRE(cuda::std::is_same_v<cudax::cufile_ref::off_type, ::off_t>);
+
+  // 2. Test default constructor.
+  STATIC_REQUIRE(!cuda::std::is_default_constructible_v<cudax::cufile_ref>);
+
+  // 3. Test cufile_ref(CUfileHandle_t) constructor.
+  STATIC_REQUIRE(cuda::std::is_nothrow_constructible_v<cudax::cufile_ref, CUfileHandle_t>);
+  STATIC_REQUIRE(cuda::std::is_convertible_v<CUfileHandle_t, cudax::cufile_ref>);
+  {
+    cudax::cufile file{filename, cudax::cufile_open_mode::out};
+
+    cudax::cufile_ref file_ref{file.get()};
+    REQUIRE(file_ref.get() == file.get());
+  }
+  test_remove_file(filename);
+
+  // 4. Test copy constructor.
+  STATIC_REQUIRE(cuda::std::is_trivially_copy_constructible_v<cudax::cufile_ref>);
+
+  // 5. Test move constructor.
+  STATIC_REQUIRE(cuda::std::is_trivially_move_constructible_v<cudax::cufile_ref>);
+
+  // 6. Test copy assignment.
+  STATIC_REQUIRE(cuda::std::is_trivially_copy_assignable_v<cudax::cufile_ref>);
+
+  // 7. Test move assignment.
+  STATIC_REQUIRE(cuda::std::is_trivially_move_assignable_v<cudax::cufile_ref>);
+
+  // 8. Test destructor.
+  STATIC_REQUIRE(cuda::std::is_trivially_destructible_v<cudax::cufile_ref>);
+
+  // 9. Test get().
+  STATIC_REQUIRE(noexcept(cuda::std::declval<cudax::cufile_ref>().get()));
+  STATIC_REQUIRE(cuda::std::is_same_v<CUfileHandle_t, decltype(cuda::std::declval<cudax::cufile_ref>().get())>);
+  {
+    const cudax::cufile file;
+    REQUIRE(cudax::cufile_ref{file}.get() == nullptr);
+  }
+  {
+    cudax::cufile file{filename, cudax::cufile_open_mode::out};
+    REQUIRE(cudax::cufile_ref{file}.get() != nullptr);
+  }
+  test_remove_file(filename);
+}