[CCCL] 瘦身 + 补全: 移除 cudax/python/libcudacxx-tests 冗余文件, 新增 c2h 测试助手 + cmake 构建系统 + 8 个 CUDA thrust examples

变更摘要:
- 删除: cudax/ (783 files, 7.2M) — 实验性组件，竞赛不需要
- 删除: python/ (226 files, 2.0M) — Python 绑定，竞赛不需要
- 删除: libcudacxx/{test,benchmarks,codegen,cmake,share} (4432 files, 31M)
  保留: libcudacxx/include/ (1463 headers, cuda::std 编译依赖)
- 新增: c2h/ (27 files) — CUB Catch2 测试辅助头文件，编译 243 个测试必需
- 新增: cmake/ (29 files) — CCCL 原生 CMake 构建系统
- 新增: thrust/examples/cuda/ (7 files) + cpp_integration/ (1 file)
  async_reduce, custom_temporary_allocation, explicit_cuda_stream,
  global_device_vector, range_view, unwrap_pointer, wrap_pointer, device

结果: cccl_upstream 从 74M→35M (瘦身 53%), 核心内容 100% 保留:
  27/27 tuning headers, 78 benchmarks, 243 tests,
  60 thrust examples, 18 CUB examples, 全部编译头文件

cccl_upstream/cudax/test/places/CMakeLists.txt

@@ -1,136 +0,0 @@
-set(
-  places_test_sources
-  include_only.cu
-  data_place_alloc.cu
-  data_place_vmm.cu
-  exec_place_scope.cu
-  placement.cu
-  stream_pool.cu
-)
-
-set(places_fail_tests exec_place_scope_data_place_fail.cu)
-
-set(
-  places_unittested_headers
-  cuda/experimental/__places/cute_partition.cuh
-  cuda/experimental/__places/places.cuh
-  cuda/experimental/__places/exec/cuda_context.cuh
-  cuda/experimental/__places/exec/green_context.cuh
-  cuda/experimental/__places/partitions/blocked_partition.cuh
-  cuda/experimental/__places/partitions/cyclic_shape.cuh
-  cuda/experimental/__places/partitions/tiled_partition.cuh
-)
-
-cccl_get_cudatoolkit()
-
-## cudax_add_places_test
-#
-# Add a places test executable and register it with ctest.
-#
-# target_name_var: Variable name to overwrite with the name of the test
-#   target. Useful for adding target information after creation.
-# source: The source file for the test.
-#
-function(cudax_add_places_test target_name_var source)
-  get_filename_component(dir ${source} DIRECTORY)
-  get_filename_component(filename ${source} NAME_WE)
-  if (dir)
-    set(filename "${dir}/${filename}")
-  endif()
-  string(REPLACE "/" "." test_name "${filename}")
-
-  set(test_target cudax.test.places.${test_name})
-
-  cccl_add_executable(${test_target} SOURCES ${source} ADD_CTEST)
-  cudax_places_configure_target(${test_target})
-  target_link_libraries(${test_target} PRIVATE cudax.compiler_interface)
-
-  set(${target_name_var} ${test_target} PARENT_SCOPE)
-endfunction()
-
-## cudax_add_places_unittest_header
-#
-# Add a places unittested header executable and register it with ctest.
-#
-# Unittested headers contain a set of tests that are enabled by including
-# `unittest.cuh` and defining `UNITTESTED_FILE`.
-#
-# target_name_var: Variable name to overwrite with the name of the test
-#   target. Useful for adding target information after creation.
-# source: The source file for the test.
-#
-function(cudax_add_places_unittest_header target_name_var source)
-  get_filename_component(relative_path ${source} DIRECTORY)
-  get_filename_component(filename ${source} NAME_WE)
-
-  string(
-    REPLACE
-    "cuda/experimental/"
-    ""
-    test_label
-    "${relative_path}/${filename}"
-  )
-  string(REPLACE "/" "." test_label "${test_label}")
-
-  set(test_target "cudax.test.places.unittest_headers.${test_label}")
-
-  get_filename_component(
-    source_full_path
-    ../../../cudax/include/${source}
-    ABSOLUTE
-  )
-  set(source ${source_full_path})
-
-  set(ut_template "${cudax_SOURCE_DIR}/cmake/places_header_unittest.in.cu")
-  set(ut_source "${cudax_BINARY_DIR}/unittest_headers/${test_target}.cu")
-  configure_file(${ut_template} ${ut_source} @ONLY)
-
-  cccl_add_executable(${test_target} SOURCES ${ut_source} ADD_CTEST)
-  cudax_places_configure_target(${test_target})
-  target_link_libraries(${test_target} PRIVATE cudax.compiler_interface)
-
-  set(${target_name_var} ${test_target} PARENT_SCOPE)
-endfunction()
-
-# Basic tests:
-foreach (source IN LISTS places_test_sources)
-  cudax_add_places_test(test_target "${source}")
-endforeach()
-
-# Unittested headers
-foreach (source IN LISTS places_unittested_headers)
-  cudax_add_places_unittest_header(test_target "${source}")
-endforeach()
-
-## cudax_add_places_fail_test
-#
-# Adds an EXCLUDE_FROM_ALL build target for `source` and a ctest that
-# verifies compilation fails with errors matching expected-error annotations
-# in the source file.
-#
-function(cudax_add_places_fail_test target_name_var source)
-  get_filename_component(filename ${source} NAME_WE)
-
-  set(test_target cudax.test.places.error.${filename})
-
-  cccl_add_executable(
-    ${test_target}
-    SOURCES ${source}
-    NO_METATARGETS
-    NO_CLANG_TIDY
-  )
-  cudax_places_configure_target(${test_target})
-  target_link_libraries(${test_target} PRIVATE cudax.compiler_interface)
-  cccl_add_xfail_compile_target_test(
-    ${test_target}
-    SOURCE_FILE "${source}"
-    ERROR_REGEX_LABEL "expected-error"
-  )
-
-  set(${target_name_var} ${test_target} PARENT_SCOPE)
-endfunction()
-
-# Expected-failure compile tests (_fail.cu convention)
-foreach (source IN LISTS places_fail_tests)
-  cudax_add_places_fail_test(test_target "${source}")
-endforeach()