Replace cudf.Series.values_host with .to_numpy().

[csadorf]

Fixes #7771

[bdice]

Approving with one question.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes

  • Improved data conversion compatibility across CPU/GPU backends, fixing issues in label/target encoding, one-hot handling, and k‑nearest classifier workflows.

• Chores

  • Standardized internal data extraction in utilities and tests to use a unified NumPy conversion path for more reliable cross-backend behavior.

Walkthrough

Replaced usages of the deprecated cuDF values_host attribute with the standard to_numpy() (and cp.asnumpy() for CuPy) across preprocessing, neighbors, testing utilities, and tests to ensure consistent array extraction without changing control flow or public method signatures.

Changes

Cohort / File(s)	Summary
Preprocessing python/cuml/cuml/preprocessing/LabelEncoder.py, python/cuml/cuml/preprocessing/TargetEncoder.py, python/cuml/cuml/preprocessing/encoders.py	Replaced .values_host accesses with .to_numpy() when converting cuDF Series to NumPy arrays (inverse_transform, fit-transform median path, and feature name generation).
Neighbors (dask) python/cuml/cuml/dask/neighbors/kneighbors_classifier.py	Unified unique-label extraction to use .to_numpy() for pandas/cuDF Series and cp.asnumpy() for CuPy arrays; removed cuDF-specific values_host branch.
Testing utilities python/cuml/cuml/testing/utils.py	from_df_to_numpy() non-DataFrame branch now uses .to_numpy() instead of .values_host for column conversion.
Tests python/cuml/tests/test_one_hot_encoder.py, python/cuml/tests/test_train_test_split.py	Replaced .values_host with .to_numpy() in test conversions and comparisons; minor copyright year update in one test.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% 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
Title check	✅ Passed	The title clearly and concisely describes the main change: replacing cudf.Series.values_host with .to_numpy().
Description check	✅ Passed	The description references the linked issue #7771, which directly relates to the changeset addressing the cuDF values_host deprecation.
Linked Issues check	✅ Passed	All code changes systematically replace .values_host with .to_numpy() across multiple files, directly addressing the requirement in issue #7771 to prevent FutureWarning failures.
Out of Scope Changes check	✅ Passed	All changes are scoped to replacing .values_host with .to_numpy() as required; only incidental copyright year update in test file is present.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[csadorf]

/merge