[INFRA] Import NVIDIA/CCCL upstream as optimization reference library

CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0

cccl_upstream/c/parallel/test/CMakeLists.txt

@@ -0,0 +1,56 @@
+cccl_get_c2h()
+
+function(cccl_c_parallel_add_test target_name_var source)
+  get_filename_component(target_name "${source}" NAME_WE)
+  string(
+    REGEX REPLACE
+    "test_([^.]*)"
+    "cccl.c.parallel.test.\\1"
+    target_name
+    "${target_name}"
+  )
+  set(target_name_var ${target_name} PARENT_SCOPE)
+
+  cccl_add_executable(
+    ${target_name}
+    ADD_CTEST
+    NO_METATARGETS
+    DIALECT 20
+    SOURCES "${source}"
+  )
+
+  set_target_properties(${target_name} PROPERTIES CUDA_RUNTIME_LIBRARY STATIC)
+  target_link_libraries(
+    ${target_name}
+    PRIVATE
+      cccl.compiler_interface
+      cccl.c.parallel
+      CUDA::cudart_static
+      CUDA::nvrtc
+      cccl.c2h.main
+  )
+
+  # Get the first CUDA include directory only
+  list(GET CUDAToolkit_INCLUDE_DIRS 0 CUDA_FIRST_INCLUDE_DIR)
+  target_compile_definitions(
+    ${target_name}
+    PRIVATE
+      TEST_CUB_PATH="-I${CCCL_SOURCE_DIR}/cub"
+      TEST_THRUST_PATH="-I${CCCL_SOURCE_DIR}/thrust"
+      TEST_LIBCUDACXX_PATH="-I${CCCL_SOURCE_DIR}/libcudacxx/include"
+      TEST_CTK_PATH="-I${CUDA_FIRST_INCLUDE_DIR}"
+      TEST_INCLUDE_PATH="${CMAKE_CURRENT_SOURCE_DIR}"
+  )
+endfunction()
+
+file(
+  GLOB test_srcs
+  RELATIVE "${CMAKE_CURRENT_LIST_DIR}"
+  CONFIGURE_DEPENDS
+  *.cu
+  *.cpp
+)
+
+foreach (test_src IN LISTS test_srcs)
+  cccl_c_parallel_add_test(test_target "${test_src}")
+endforeach()