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/docs/thrust/function_objects/adaptors.rst

@@ -0,0 +1,6 @@
+.. _thrust-module-api-function-objects-adaptors:
+
+Function Object Adaptors
+-------------------------
+
+  - :cpp:class:`thrust::zip_function <thrust::zip_function>`

cccl_upstream/docs/thrust/function_objects/placeholder.rst

@@ -0,0 +1,10 @@
+.. _thrust-module-api-function-objects-placeholder:
+
+Placeholder Objects
+--------------------
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   ../api/*placeholder*

cccl_upstream/docs/thrust/function_objects/predefined.rst

@@ -0,0 +1,11 @@
+.. _thrust-module-api-function-objects-predefined:
+
+Function Objects
+----------------
+
+Users are encouraged to use the standard C++ function objects available from `<cuda/std/functional>`.
+Thrust provides the following additional function objects:
+
+  - :cpp:struct:`thrust::square <thrust::square>`
+  - :cpp:struct:`thrust::project1st <thrust::project1st>`
+  - :cpp:struct:`thrust::project2nd <thrust::project2nd>`