Remove all decorator usage of dask.delayed

[jcrist]

We've been seeing some odd cloudpickle failures periodically in our dask test suite. While I'm not able to fully describe the error, I suspect this is a bug in cloudpickle around serializing dask.delayed decorated functions.

In brief:

• A function defined as a top-level function or a staticmethod on a top-level class is trivially serializable with pickle (no cloudpickle needed).
• Closures (functions defined within a function) will require cloudpickle. As will functions decorated with dask.delayed (since the top-level name no longer is the function but rather a Delayed object, breaking default serialization of the nested object).

Previously we could rely on cloudpickle to handle both these cases without issue, so preferring the simpler objects was more about efficiency (both time and serialized message size) than about correctness. However, the periodic failures make me suspect a cloudpickle bug. To test this, I'm removing all remaining locations I could find that might trigger this issue. If we see another failure later then we can investigate this more then.

Fixes #8487.

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Improved reliability when retrieving remote model attributes in distributed workflows.
  • Enhanced conversion of non-2D distributed inputs to compatible tabular formats.
  • Preserved accurate distributed Naive Bayes scoring across data partitions.

Walkthrough

The changes move Dask delayed wrapping to call sites, broaden non-2D partition conversion to cudf.Series, and extract Naive Bayes accuracy counting into a module-level helper.

Changes

Dask delayed task handling

Layer / File(s)	Summary
Model attribute access python/cuml/cuml/dask/common/base.py	_get_model_attr remains a regular helper. __getattr__ now applies dask.delayed before computing remote attribute access.
Partition conversion python/cuml/cuml/dask/common/dask_arr_utils.py	_to_cudf uses call-site delayed wrapping and returns cudf.Series for non-2D inputs. The copyright range now ends in 2026.
Naive Bayes scoring python/cuml/cuml/dask/naive_bayes/naive_bayes.py	score uses a module-level _count_accurate_predictions helper through a delayed wrapper for each partition.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🔵 Low · up to 98264

Higher-dimensional inputs may currently reach conversion without a clear rejection, causing incorrect or confusing behavior for direct callers. The PR is otherwise mergeable, but this bounded correctness case should be fixed or explicitly accepted before merge.

Suggested reviewers: divyegala

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The _to_cudf change alters non-2D input conversion behavior, which is not required by the linked serialization issue.	Revert the unrelated non-2D input conversion behavior change, or document and link it to a separate requirement.
Docstring Coverage	⚠️ Warning	Docstring coverage is 37.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the primary change: removing dask.delayed decorator usage.
Description check	✅ Passed	The description explains the serialization issue, the planned decorator removal, and the linked issue.
Linked Issues check	✅ Passed	The changes remove dask.delayed decorators and preserve call-site behavior, directly addressing the serialization failure in issue #8487.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@python/cuml/cuml/dask/common/dask_arr_utils.py`:
- Line 97: Update to_dask_cudf to branch on the input array’s ndim: convert 1-D
input with cudf.Series, 2-D input with cudf.DataFrame, and raise ValueError for
higher-dimensional input before conversion. Add coverage for 1-D, 2-D, and
invalid inputs.

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Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between c17776b and 9826470.

📒 Files selected for processing (3)

• python/cuml/cuml/dask/common/base.py
• python/cuml/cuml/dask/common/dask_arr_utils.py
• python/cuml/cuml/dask/naive_bayes/naive_bayes.py

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[csadorf]

[csadorf]

/merge