Hide internal C++ symbols exported from libcuopt

[bdice]

Summary

libcuopt.so currently exports a large internal C++/CUDA symbol surface, including CUB/Thrust/RAFT/RMM symbols and cuOpt detail implementation symbols. This matches the RAPIDS-wide symbol visibility problem tracked in rapidsai/build-infra#53.

Evidence

Local audit of cpp/build/latest/libcuopt.so with readelf --dyn-syms --wide | c++filt found approximately:

• 10,383 defined dynamic symbols
• 2,020 cub:: symbols
• 2,318 thrust:: symbols
• 1,028 raft:: symbols
• 2,691 rmm:: symbols
• 2,628 cuopt::linear_programming::detail symbols
• 1,574 cuopt::routing::detail symbols
• 376 grpc:: symbols
• 361 google::protobuf symbols
• 579 tbb:: symbols

detect-weak-linking (https://github.com/rapidsai/detect-weak-linking) did not report default weak CUDA kernel duplicates for the sampled test executable, but compute-sanitizer reports duplicate CUB kernel registration in test runs and the broad exported-symbol surface increases collision risk.

Desired direction

Follow the treatment used in RAPIDS libraries such as cuML, cuDF, RAFT, and RMM:

• Set hidden-by-default visibility for cuOpt shared library targets.
• Add a CUOPT_EXPORT macro for public ABI symbols.
• Mark public C API declarations and any public C++ API/types/template instantiations that must remain visible.
• Add a CI/package symbol check similar to cuDF's ci/check_symbols.sh, with cuOpt-specific forbidden export patterns.

References

• rapidsai/build-infra#53
• Fix symbol export rapidsai/cuml#8037
• Hide visibility of non public symbols rapidsai/cudf#15982
• Fix symbol export rapidsai/raft#3006
• Explicitly mark RMM headers with RMM_EXPORT rapidsai/rmm#1654