[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/install/cccl.cmake

@@ -0,0 +1 @@
+cccl_generate_install_rules(CCCL ${CCCL_TOPLEVEL_PROJECT} NO_HEADERS PACKAGE)

cccl_upstream/cmake/install/cub.cmake

@@ -0,0 +1,6 @@
+cccl_generate_install_rules(
+  CUB
+  ${CCCL_TOPLEVEL_PROJECT}
+  HEADERS_INCLUDE "*.cuh"
+  PACKAGE
+)

cccl_upstream/cmake/install/cudax.cmake

@@ -0,0 +1,7 @@
+cccl_generate_install_rules(
+  cudax
+  ${CCCL_ENABLE_CUDAX}
+  HEADERS_SUBDIRS "include/cuda"
+  HEADERS_INCLUDE "*.cuh"
+  PACKAGE
+)

cccl_upstream/cmake/install/libcudacxx.cmake

@@ -0,0 +1,8 @@
+cccl_generate_install_rules(
+  libcudacxx
+  ${CCCL_TOPLEVEL_PROJECT}
+  HEADERS_SUBDIRS "include/cuda" "include/nv"
+  HEADERS_INCLUDE "*"
+  HEADERS_EXCLUDE "CMakeLists.txt"
+  PACKAGE
+)

cccl_upstream/cmake/install/thrust.cmake

@@ -0,0 +1,6 @@
+cccl_generate_install_rules(
+  Thrust
+  ${CCCL_TOPLEVEL_PROJECT}
+  HEADERS_INCLUDE "*.h" "*.inl"
+  PACKAGE
+)