[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/execution/test_completion_signatures.cu

@@ -1,140 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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 this first
-#include <cuda/experimental/execution.cuh>
-
-// Then include the test helpers
-#include "testing.cuh" // IWYU pragma: keep
-
-// NOLINTBEGIN(misc-unused-using-decls)
-using cuda::experimental::execution::completion_signatures;
-using cuda::experimental::execution::set_error;
-using cuda::experimental::execution::set_error_t;
-using cuda::experimental::execution::set_stopped;
-using cuda::experimental::execution::set_stopped_t;
-using cuda::experimental::execution::set_value;
-using cuda::experimental::execution::set_value_t;
-// NOLINTEND(misc-unused-using-decls)
-
-namespace
-{
-C2H_TEST("", "[utilities][completion_signatures]")
-{
-  STATIC_REQUIRE(completion_signatures{} == completion_signatures{});
-  STATIC_REQUIRE_FALSE(completion_signatures{} != completion_signatures{});
-}
-
-// Additional tests for completion_signatures
-C2H_TEST("completion_signatures_basic", "[utilities][completion_signatures]")
-{
-  constexpr auto cs_empty   = completion_signatures<>{};
-  constexpr auto cs_value   = completion_signatures<set_value_t(int)>{};
-  constexpr auto cs_error   = completion_signatures<set_error_t(float)>{};
-  constexpr auto cs_stopped = completion_signatures<set_stopped_t()>{};
-  constexpr auto cs_all     = completion_signatures<set_value_t(int), set_error_t(float), set_stopped_t()>{};
-
-  // Test size
-  STATIC_REQUIRE(cs_empty.size() == 0);
-  STATIC_REQUIRE(cs_value.size() == 1);
-  STATIC_REQUIRE(cs_all.size() == 3);
-
-  // Test contains
-  STATIC_REQUIRE(cs_value.contains(static_cast<set_value_t (*)(int)>(nullptr)));
-  STATIC_REQUIRE_FALSE(cs_value.contains(static_cast<set_error_t (*)(float)>(nullptr)));
-  STATIC_REQUIRE(cs_all.contains(static_cast<set_stopped_t (*)()>(nullptr)));
-
-  // Test count
-  STATIC_REQUIRE(cs_all.count(set_value) == 1);
-  STATIC_REQUIRE(cs_all.count(set_error) == 1);
-  STATIC_REQUIRE(cs_all.count(set_stopped) == 1);
-
-  // Test operator==
-  STATIC_REQUIRE(cs_value == cs_value);
-  STATIC_REQUIRE_FALSE(cs_value == cs_error);
-  STATIC_REQUIRE(cs_empty == cs_empty);
-  STATIC_REQUIRE(cs_all == cs_all);
-  STATIC_REQUIRE(completion_signatures<set_value_t(int), set_error_t(float)>{}
-                 == completion_signatures<set_error_t(float), set_value_t(int)>{});
-
-  // Test operator!=
-  STATIC_REQUIRE(cs_value != cs_error);
-  STATIC_REQUIRE_FALSE(cs_all != cs_all);
-
-  // Test operator+
-  STATIC_REQUIRE((cs_value + cs_error) == completion_signatures<set_value_t(int), set_error_t(float)>{});
-  STATIC_REQUIRE((cs_empty + cs_value) == cs_value);
-  STATIC_REQUIRE((cs_value + cs_empty) == cs_value);
-
-  // Test operator-
-  STATIC_REQUIRE((cs_all - cs_value) == completion_signatures<set_error_t(float), set_stopped_t()>{});
-  STATIC_REQUIRE((cs_all - cs_error) == completion_signatures<set_value_t(int), set_stopped_t()>{});
-  STATIC_REQUIRE((cs_all - cs_stopped) == completion_signatures<set_value_t(int), set_error_t(float)>{});
-  STATIC_REQUIRE((cs_all - cs_all) == completion_signatures<>{});
-  STATIC_REQUIRE((cs_value - cs_error) == cs_value);
-}
-
-// Test select
-C2H_TEST("completion_signatures_select", "[utilities][completion_signatures]")
-{
-  constexpr auto cs = completion_signatures<set_value_t(int), set_error_t(float), set_stopped_t()>{};
-
-  // select(set_value) should return only set_value_t(int)
-  constexpr auto v = cs.select(set_value);
-  STATIC_REQUIRE(v.size() == 1);
-  STATIC_REQUIRE(v.contains<set_value_t(int)>());
-
-  // select(set_error) should return only set_error_t(float)
-  constexpr auto e = cs.select(set_error);
-  STATIC_REQUIRE(e.size() == 1);
-  STATIC_REQUIRE(e.contains<set_error_t(float)>());
-
-  // select(set_stopped) should return only set_stopped_t()
-  constexpr auto s = cs.select(set_stopped);
-  STATIC_REQUIRE(s.size() == 1);
-  STATIC_REQUIRE(s.contains<set_stopped_t()>());
-}
-
-// Test filter
-struct filter_value_only
-{
-  template <class Sig>
-  constexpr bool operator()(Sig*) const noexcept
-  {
-    return cuda::experimental::execution::__detail::__signature_disposition<Sig>
-        == cuda::experimental::execution::__disposition::__value;
-  }
-};
-
-C2H_TEST("completion_signatures_filter", "[utilities][completion_signatures]")
-{
-  constexpr auto cs       = completion_signatures<set_value_t(int), set_error_t(float), set_stopped_t()>{};
-  constexpr auto filtered = cs.filter(filter_value_only{});
-  STATIC_REQUIRE(filtered.size() == 1);
-  STATIC_REQUIRE(filtered.contains<set_value_t(int)>());
-}
-
-// Test apply
-struct count_signatures
-{
-  template <class... Sigs>
-  constexpr int operator()(Sigs*...) const noexcept
-  {
-    return sizeof...(Sigs);
-  }
-};
-
-C2H_TEST("completion_signatures_apply", "[utilities][completion_signatures]")
-{
-  constexpr auto cs   = completion_signatures<set_value_t(int), set_error_t(float), set_stopped_t()>{};
-  constexpr int count = cs.apply(count_signatures{});
-  STATIC_REQUIRE(count == 3);
-}
-} // namespace