build(cmake): stop compiling routing/mathopt sources twice

[ramakrishnap-nv]

cuopt_routing and cuopt_mathopt were compiled directly from source, while cuopt_objs separately recompiled the same files a second time just to feed cuopt_static. Gives routing/mathopt the same OBJECT-library treatment cuopt_client already uses, so each domain compiles once and cuopt_static links the objects instead of rebuilding them. Removes cuopt_objs.

Also fixes an ordering bug this touched: CUDSS_MT_LIB_FILE_NAME was recomputed after cuopt_mathopt's compile definitions had already captured the stale value.

Verified locally: full build succeeds, ninja target count drops 631 → 350.

Verified in CI (conda-cpp-build / 13.3.0, amd64): 631 → 474 targets, 0 errors, 0 failed distributed compilations.

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ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between 8a25c92 and f9c346d.

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• cpp/CMakeLists.txt

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📝 Walkthrough

Walkthrough

CMake now builds routing and mathopt through hidden-visibility object libraries. Shared targets receive their dependencies during assembly. Static builds embed the component objects directly.

Changes

Component build restructuring

Layer / File(s)	Summary
Object library and routing setup cpp/CMakeLists.txt	CMake documents visibility for component object libraries. It adds optional cuDSS threading-layer construction and builds cuopt_routing from cuopt_routing_objs with routing settings and dependencies.
Mathopt and static target assembly cpp/CMakeLists.txt	CMake moves mathopt settings and KaMinPar requirements to cuopt_mathopt_objs, links PSLP, Highway, and KaMinPar on cuopt_mathopt, and embeds component objects in cuopt_static.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Refactor

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely describes the primary change: preventing routing and mathopt sources from being compiled twice in the CMake build.
Description check	✅ Passed	The description directly explains the build-graph changes, the removal of duplicate compilation, the CUDSS_MT_LIB_FILE_NAME ordering fix, and verification results.

✨ Finishing Touches 💡 1

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CI Test Summary

✅ All 32 test job(s) passed.

[ramakrishnap-nv]

/merge