fix: broadcast scalar axis args to match array sample length in Mean/WeightedMean fill

[Copilot]

• Understand the issue: scalar axis args fail with array samples in Mean/WeightedMean storage
• Add broadcasting of scalar positional args to match sample array length in fill method
• Add tests for the new behavior in test_profiles.py
• Run tests to verify the fix - all pass
• Code review - addressed comment about using np.ndim for general array check
• Run prek -a and fix mypy type errors (added type: ignore annotations and is not None guard)
• Security scan - no alerts found

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[henryiii]

@copilot, please run prek -a (pip install prek if needed) and fix up the issues there.

[Copilot]

@copilot, please run prek -a (pip install prek if needed) and fix up the issues there.

Fixed in 7310c9d. prek -a now passes — added is not None guard and # type: ignore annotations to resolve the 3 mypy errors on the broadcast logic.

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[Copilot]

Pull request overview

This PR fixes filling Mean/WeightedMean histograms when positional axis arguments are scalars but sample is an array-like, by broadcasting those scalar axis arguments to the sample length (addressing issue #727).

Changes:

• Add scalar positional-arg broadcasting in Histogram.fill when sample is array-like.
• Improve _fill_cast typing via overloads and remove some type-ignores.
• Add regression tests covering scalar-axis + array-sample filling for Mean and WeightedMean storages.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/boost_histogram/histogram.py	Broadcast scalar positional args based on sample length; tighten typing for _fill_cast; adjust threaded split casting.
tests/test_profiles.py	Add tests validating scalar-axis broadcast behavior for Mean/WeightedMean storages.

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