[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/thrust/examples/run_length_encoding.cu

@@ -0,0 +1,54 @@
+#include <thrust/copy.h>
+#include <thrust/device_vector.h>
+#include <thrust/reduce.h>
+
+#include <cuda/iterator>
+
+#include <iostream>
+#include <iterator>
+
+// This example computes a run-length code [1] for an array of characters.
+//
+// [1] http://en.wikipedia.org/wiki/Run-length_encoding
+
+int main()
+{
+  // input data on the host
+  const char data[] = "aaabbbbbcddeeeeeeeeeff";
+
+  const size_t N = (sizeof(data) / sizeof(char)) - 1;
+
+  // copy input data to the device
+  thrust::device_vector<char> input(data, data + N);
+
+  // allocate storage for output data and run lengths
+  thrust::device_vector<char> output(N);
+  thrust::device_vector<int> lengths(N);
+
+  // print the initial data
+  std::cout << "input data:" << '\n';
+  thrust::copy(input.begin(), input.end(), std::ostream_iterator<char>(std::cout, ""));
+  std::cout << '\n' << '\n';
+
+  // compute run lengths
+  size_t num_runs =
+    thrust::reduce_by_key(
+      input.begin(),
+      input.end(), // input key sequence
+      cuda::constant_iterator<int>(1), // input value sequence
+      output.begin(), // output key sequence
+      lengths.begin() // output value sequence
+      )
+      .first
+    - output.begin(); // compute the output size
+
+  // print the output
+  std::cout << "run-length encoded output:" << '\n';
+  for (size_t i = 0; i < num_runs; i++)
+  {
+    std::cout << "(" << output[i] << "," << lengths[i] << ")";
+  }
+  std::cout << '\n';
+
+  return 0;
+}