#63170 - fix array.py

[ahalsey]

Update _reduce_calc to consistently return the correct datetime format as mentioned in issue 63170

• closes BUG: Arrow duration reduction consistency #63170 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

[mroeschke]

Thanks for the PR, but the issue still Needs Discussion for the expected behavior before proceeding so closing in the meantime