Avoid pickling lambda in dask LabelBinarizer pytests

[aamijar]

Resolves #7241

    |     result = pickle.dumps(x, **dump_kwargs)
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    | AttributeError: Can't get local object 'test_basic_functions.<locals>.<lambda>'

To prevent this error and the following exception handling altogether we can avoid using a lambda.

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• python/cuml/tests/dask/test_dask_label_binarizer.py

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📝 Walkthrough

Summary by CodeRabbit

• Tests
  • Refactored internal test utilities for improved code clarity and maintainability.

Walkthrough

This change refactors a test file by extracting an inline lambda function into a named helper function _get_block(x) that returns x.get(). The helper is used in a map_blocks operation to retrieve values from Dask/CuPy blocks during test execution.

Changes

Cohort / File(s)	Summary
Test Helper Refactoring python/cuml/tests/dask/test_dask_label_binarizer.py	Extracted inline lambda into named helper function _get_block(x) for retrieving block values; preserves dtype handling and transformation workflow.

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🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 a lambda with a named function to avoid pickling issues in the dask LabelBinarizer tests.
Description check	✅ Passed	The description is directly related to the changeset, referencing the linked issue and explaining the motivation for avoiding the lambda to prevent pickle serialization errors.
Linked Issues check	✅ Passed	The code changes directly address the root cause identified in issue #7241 by replacing the problematic lambda with a named function _get_block to prevent pickle errors.
Out of Scope Changes check	✅ Passed	All changes are scoped to the dask LabelBinarizer test file and directly address the lambda pickling issue; no extraneous modifications are present.

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[jcrist]

Dask uses cloudpickle, which can serialize lambdas just fine. It's very weird that we see issues here only sometimes, rather than always or never.

That said, this fix isn't wrong, it just shouldn't be necessary. Happy to merge, but I suspect there's something else sneaky going on here.

[jcrist]

This needs #7901 before tests will pass.

[aamijar]

/merge