Remove deprecated API cudf::nans_to_nulls

[davidwendt]

Description

Removes the deprecated function cudf::nans_to_nulls which is replaced by cudf::column_nans_to_nulls.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[PointKernel]

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Run ID: e000aa29-ac4b-401d-a981-5ce40fa2d0f4

📥 Commits

Reviewing files that changed from the base of the PR and between 450b24a and ce62970.

📒 Files selected for processing (8)

• cpp/include/cudf/transform.hpp
• cpp/src/transform/nans_to_nulls.cu
• python/cudf_polars/cudf_polars/containers/column.py
• python/pylibcudf/pylibcudf/libcudf/transform.pxd
• python/pylibcudf/pylibcudf/transform.pxd
• python/pylibcudf/pylibcudf/transform.pyi
• python/pylibcudf/pylibcudf/transform.pyx
• python/pylibcudf/tests/test_transform.py

💤 Files with no reviewable changes (6)

• python/pylibcudf/pylibcudf/transform.pyi
• python/pylibcudf/pylibcudf/transform.pxd
• python/pylibcudf/pylibcudf/transform.pyx
• cpp/include/cudf/transform.hpp
• python/pylibcudf/pylibcudf/libcudf/transform.pxd
• cpp/src/transform/nans_to_nulls.cu

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📝 Summary

Summary by CodeRabbit

• New Features

  • Added a column-based NaN-to-null conversion interface that returns a complete column.
  • NaN values are converted to null while existing null values are preserved.
  • Empty inputs remain supported, and non-floating-point inputs are rejected.

• Breaking Changes

  • Removed the previous NaN-to-null interface that returned a null mask and null count.
  • Updated Python column masking to use the column-based conversion behavior.

Walkthrough

The NaN-to-null conversion surface now uses a column-returning API. C++ declarations, Python bindings, and Polars integration no longer use the removed mask-and-count API.

Changes

NaN-to-null conversion migration

Layer / File(s)	Summary
C++ column conversion API cpp/include/cudf/transform.hpp, cpp/src/transform/nans_to_nulls.cu	Replaces nans_to_nulls with column_nans_to_nulls, which returns a column with NaNs converted to nulls and existing nulls preserved.
Python binding API cleanup python/pylibcudf/pylibcudf/libcudf/transform.pxd, python/pylibcudf/pylibcudf/transform.*	Removes the obsolete nans_to_nulls declarations, wrapper, and export.
Polars integration and test cleanup python/cudf_polars/cudf_polars/containers/column.py, python/pylibcudf/tests/test_transform.py	Updates Column.mask_nans to use column_nans_to_nulls. Removes the obsolete test and updates the copyright notice.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to ce629

The API migration updates the shown consumer to the replacement column-returning interface, with no actionable current-head risk identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	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 states that the deprecated cudf::nans_to_nulls API is removed. It matches the main change.
Description check	✅ Passed	The description accurately explains that cudf::nans_to_nulls is removed and replaced by cudf::column_nans_to_nulls. It is related to the changeset.
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.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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