[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/cmake/CCCLHideThirdPartyOptions.cmake

@@ -0,0 +1,39 @@
+mark_as_advanced(
+  BUILD_TESTING
+  CATCH_BUILD_EXAMPLES
+  CATCH_BUILD_EXTRA_TESTS
+  CATCH_BUILD_STATIC_LIBRARY
+  CATCH_BUILD_TESTING
+  CATCH_ENABLE_COVERAGE
+  CATCH_ENABLE_WERROR
+  CATCH_INSTALL_DOCS
+  CATCH_INSTALL_HELPERS
+  CATCH_USE_VALGRIND
+  CLANG_FORMAT
+  CLANG_TIDY
+  CPM_DONT_CREATE_PACKAGE_LOCK
+  CPM_DONT_UPDATE_MODULE_PATH
+  CPM_DOWNLOAD_ALL
+  CPM_INCLUDE_ALL_IN_PACKAGE_LOCK
+  CPM_LOCAL_PACKAGES_ONLY
+  CPM_SOURCE_CACHE
+  CPM_USE_LOCAL_PACKAGES
+  CPM_USE_NAMED_CACHE_DIRECTORIES
+  CPPCHECK
+  CUB_DIR
+  FETCHCONTENT_BASE_DIR
+  FETCHCONTENT_FULLY_DISCONNECTED
+  FETCHCONTENT_QUIET
+  FETCHCONTENT_SOURCE_DIR_CATCH2
+  FETCHCONTENT_UPDATES_DISCONNECTED
+  FETCHCONTENT_UPDATES_DISCONNECTED_CATCH2
+  LIBCXX_CXX_ABI
+  LIT_EXTRA_ARGS
+  LLVM_DEFAULT_EXTERNAL_LIT
+  LLVM_DEFAULT_TARGET_TRIPLE
+  LLVM_EXTERNAL_LIT
+  LLVM_HOST_TRIPLE
+  LLVM_PATH
+  Thrust_DIR
+  libcudacxx_DIR
+)