Updated docstrings in pymc.step_methods.arraystep.py

[lejenhan]

Description

Related Issue

• Closes #
• Related to Update docstrings for better rendering on website and numpydoc compliance #5459

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

Note: Updated docstrings in pymc.step_methods.arraystep.py, which may not be part of the public API but improves clarity and maintains consistency with numpydoc conventions.

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📚 Documentation preview 📚: https://pymc--7796.org.readthedocs.build/en/7796/

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