feat(cccl): integrate missing CCCL directories — python/, ci/, .agent/, docs/, test/

Sparse-checkout from NVIDIA/cccl main branch to complete cccl_upstream:

Added:
- python/cuda_cccl/ (226 files) — Python bindings for device-level algorithms
  Critical for muh toolchain: cuda.compute.reduce_into, scan, radix_sort, etc.
  Includes 204 .py files with full test coverage for all 27 algorithms
- ci/ (163 files) — Build/test infrastructure
  build_cub.sh, test_cub.sh, build_and_test_targets.sh, matrix.yaml
  Directly maps to our [INFRA-CI] and [INFRA-BUILD] items
- .agent/skills/ (7 files) — NVIDIA's own agent skills for CCCL
  cccl-style/SKILL.md, cccl-test/SKILL.md, sass-diff/SKILL.md
- docs/ (491 files) — Official CCCL documentation
  CI references, CMake guides, Python compute docs, libcudacxx PTX docs
- test/ (12 files) — Top-level integration tests (cuda_smoke, stdpar)
- Root configs: .clang-format, .clang-tidy, CONTRIBUTING.md, pyproject.toml
- CLAUDE.md symlink → AGENTS.md (NVIDIA's standard)

cccl_upstream now mirrors full NVIDIA/cccl structure:
  Before: 42M (cub + thrust + libcudacxx + cudax + c + examples + benchmarks)
  After:  53M (+python +ci +docs +.agent +test +configs)

This completes the CCCL base needed for:
- [muh-bench] items: ci/util/build_and_test_targets.sh for targeted builds
- [CCCL-verify] items: python/cuda_cccl/tests/ as reference implementations
- [CCCL-test] items: ci/test_cub.sh, ci/test_thrust.sh
- Agent workflow: .agent/skills/ for consistent style and test patterns

cccl_upstream/ci/windows/test_thrust.ps1

@@ -0,0 +1,62 @@
+Param(
+    [Parameter(Mandatory = $false)]
+    [Alias("std")]
+    [ValidateNotNullOrEmpty()]
+    [ValidateSet(17, 20)]
+    [int]$CXX_STANDARD = 17,
+    [Parameter(Mandatory = $false)]
+    [Alias("arch")]
+    [string]$CUDA_ARCH = "",
+    [Parameter(Mandatory = $false)]
+    [Alias("cpu-only")]
+    [switch]$CPU_ONLY = $false,
+    [Parameter(Mandatory = $false)]
+    [Alias("gpu-only")]
+    [switch]$GPU_ONLY = $false,
+    [Parameter(Mandatory = $false)]
+    [Alias("cmake-options")]
+    [string]$CMAKE_OPTIONS = ""
+)
+
+$ErrorActionPreference = "Stop"
+
+$CURRENT_PATH = Split-Path $pwd -leaf
+If($CURRENT_PATH -ne "ci") {
+    Write-Host "Moving to ci folder"
+    pushd "$PSScriptRoot/.."
+}
+
+if ($CPU_ONLY) {
+    $artifactTag = "test_cpu"
+    $presets = @("thrust-cpu")
+} elseif ($GPU_ONLY) {
+    $artifactTag = "test_gpu"
+    $presets = @("thrust-gpu")
+} else {
+    if ($env:GITHUB_ACTIONS) {
+        throw "Error: test_thrust.ps1 requires -cpu-only or -gpu-only in CI"
+    }
+    $artifactTag = ""
+    $presets = @("thrust-cpu", "thrust-gpu")
+}
+
+if ($env:GITHUB_ACTIONS -and $artifactTag) {
+    $producerId = (& bash "./util/workflow/get_producer_id.sh").Trim()
+    $artifactName = "z_thrust-test-artifacts-$env:DEVCONTAINER_NAME-$producerId-$artifactTag"
+    Write-Host "Unpacking artifact '$artifactName'"
+    & bash "./util/artifacts/download_packed.sh" "$artifactName" "../"
+} else {
+    $cmd = "$PSScriptRoot/build_thrust.ps1 -std $CXX_STANDARD -arch '$CUDA_ARCH' -cmake-options '$CMAKE_OPTIONS'"
+    Write-Host "Running: $cmd"
+    Invoke-Expression $cmd
+}
+
+Import-Module -Name "$PSScriptRoot/build_common.psm1" -ArgumentList @($CXX_STANDARD, $CUDA_ARCH, $CMAKE_OPTIONS)
+
+foreach ($preset in $presets) {
+    test_preset "Thrust ($preset)" $preset
+}
+
+If($CURRENT_PATH -ne "ci") {
+    popd
+}