Apply ABI Breaking Changes for KMeans

[tarang-jain]

Closes #2048

_v2 APIs were tagged to be removed in 26.08.
We also remove the inerta_check field that was marked for deprecation

[coderabbitai]

📝 Walkthrough

Walkthrough

Removes the deprecated KMeans v2 C API (types and functions), deletes the inertia_check param from headers and language bindings, simplifies internal param converters to the unified params type, updates tests to call unsuffixed APIs, and updates C/Python docs.

Changes

Remove KMeans v2 API variants

Layer / File(s)	Summary
Remove v2 params structure and inertia_check field from header c/include/cuvs/cluster/kmeans.h	Removes inertia_check from cuvsKMeansParams, deletes cuvsKMeansParams_v2 typing/docs, and drops ABI compatibility comments.
Remove v2 function declarations from header c/include/cuvs/cluster/kmeans.h	Deletes cuvsKMeansFit_v2, cuvsKMeansPredict_v2, and related v2 docs so unsuffixed signatures remain.
Simplify internal parameter converters in implementation c/src/cluster/kmeans.cpp	Replaces templated param converters with fixed overloads taking const cuvsKMeansParams& and removes template params from _fit/__predict helpers.
Remove v2 function implementations and inertia_check initialization c/src/cluster/kmeans.cpp	Removes .inertia_check initializer from cuvsKMeansParamsCreate and deletes cuvsKMeansParamsCreate_v2, Destroy_v2, Fit_v2, Predict_v2 implementations.
Update tests to call unsuffixed KMeans API c/tests/cluster/kmeans_c.cu	Removes templated test dispatchers and v2-specific test cases; tests now call cuvsKMeansParamsCreate, cuvsKMeansFit, cuvsKMeansPredict directly.
Update C API documentation fern/pages/c_api/c-api-cluster-kmeans.md	Removes v2 API sections and replacement/ABI notes referencing _v2 signatures.
Remove inertia_check from Python docs fern/pages/python_api/python-api-cluster-kmeans.md	Deletes inertia_check from the documented KMeansParams parameters and __init__ signature.
Cython bindings and implementation python/cuvs/.../kmeans.pxd, python/cuvs/.../kmeans.pyx	Removes inertia_check field from the .pxd, deletes inertia_check kwarg and warning logic from the .pyx.
Rust FFI bindings rust/cuvs-sys/src/bindings.rs	Removes inertia_check from the FFI cuvsKMeansParams struct and updates compile-time size/offset assertions to the new layout.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• rapidsai/cuvs#2070: Modifies KMeans v2 C API symbol visibility in the same header file.
• rapidsai/cuvs#2015: Earlier changes to KMeans params handling and inertia_check deprecation.
• rapidsai/cuvs#2017: Removes use of inertia_check in multi-GPU k-means implementation.

Suggested labels

breaking, cpp, Rust, improvement

Suggested reviewers

• cjnolet
• lowener
• robertmaynard

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 8.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	All linked issue requirements are met: _v2 APIs removed from C tests, header, and implementation; template ParamsT removed; inertia_check deprecated from Python API; documentation updated.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the linked issue requirements: removing _v2 APIs, deprecating inertia_check, and updating related documentation across C/Python/Rust code.
Description check	✅ Passed	The PR description clearly relates to the changeset by referencing issue #2048 and describing the removal of _v2 APIs and the inertia_check field, which align with the actual changes across multiple files.
Title check	✅ Passed	The title 'Apply ABI Breaking Changes for KMeans' accurately and directly summarizes the main objective of the PR, which is to apply C ABI breaking changes to the KMeans API by removing _v2 APIs and the inertia_check parameter.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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