[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/python/cuda_cccl/benchmarks/compute/README.md

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+# cuda.compute Benchmarks
+
+Compare Python `cuda.compute` performance against C++ CUB implementations.
+
+## Setup
+
+This project uses [pixi](https://pixi.sh) to manage environments and dependencies.
+
+Two environments are available:
+
+- **`wheel`** - Uses the released `cuda-cccl` package
+- **`source`** - Builds `cuda-cccl` from the local repository
+
+### Build C++ Benchmarks
+
+Build CUB benchmarks using the CI script (one-time, ~13 minutes):
+
+```bash
+cd /path/to/cccl
+./ci/build_cub.sh -arch 89  # Use your GPU arch (89=RTX 4090, 80=A100, 90=H100)
+```
+
+Binaries are built to: `build/cub/bin/`
+
+## Run Benchmarks
+
+### Using pixi tasks
+
+```bash
+# Run Python benchmarks (released cuda-cccl)
+pixi run -e wheel bench
+
+# Run Python benchmarks (local source build)
+pixi run -e source bench
+
+# Run Python benchmarks with reduced parameter set
+pixi run -e wheel bench-quick
+
+# Run just one benchmark
+pixi run -e wheel bench -b transform/fill
+
+# Run C++ benchmarks
+pixi run -e wheel bench-cpp
+
+# Run both Python and C++ benchmarks
+pixi run -e wheel bench-all
+```
+
+### Using run_benchmarks.py directly
+
+```bash
+# Run both C++ and Python (default)
+pixi run -e wheel python run_benchmarks.py -b transform/fill -d 0
+
+# Run only C++
+pixi run -e wheel python run_benchmarks.py -b transform/fill --cpp
+
+# Run only Python
+pixi run -e wheel python run_benchmarks.py -b transform/fill --py
+
+# Show help
+pixi run -e wheel python run_benchmarks.py --help
+```
+
+To run the benchmarks using the "quick" configuration:
+
+```bash
+pixi run -e wheel python run_benchmarks.py --quick
+```
+
+## Compare Results
+
+```bash
+pixi run -e wheel python analysis/python_vs_cpp_summary.py -b transform/fill
+```
+
+## Web Report
+
+A simple page used to visualize a set of results.
+
+- Requires `results/` to be populated with benchmark results.
+
+First generate a manifest:
+
+```bash
+pixi run -e wheel python analysis/generate_web_report_manifest.py \
+  --results-dir results \
+  --output results/manifest.json
+```
+
+Build the web report single file app:
+
+```bash
+cd analysis/web-report
+npm install
+npm run build
+```
+
+This will output a single file app to `analysis/web-report/dist/` copy it to the `results/` directory and:
+
+```bash
+cd results/
+python3 -m http.server
+```
+
+Now its possible to share the results directory as a zip/tar file.
+
+## Manual Usage
+
+### List benchmark configurations
+
+```bash
+# Python
+pixi run -e wheel python transform/fill.py --list
+
+# C++
+/path/to/cccl/build/cub/bin/cub.bench.transform.fill.base --list
+```
+
+### Run with custom options
+
+```bash
+# Python - specific type and size
+pixi run -e wheel python transform/fill.py --axis "T=I32" --axis "Elements[pow2]=20" --devices 0
+
+# C++ - save JSON
+/path/to/cccl/build/cub/bin/cub.bench.transform.fill.base \
+  --json results/transform/fill_cpp.json \
+  --devices 0
+```
+
+### Compare manually
+
+```bash
+pixi run -e wheel python analysis/python_vs_cpp_summary.py \
+  results/transform/fill_py.json \
+  results/transform/fill_cpp.json \
+  --device 0
+```
+
+## AI commands
+
+These are using the .opencode folder but can be moved to other Agents.
+
+### /migration-status
+
+Generates a report of the migration status for each benchmark in CUB.