Add public typing.py module

[micguerr-bopen]

• Closes Cannot import xarray.core.rolling with xarray version 2025.3.0 and python 3.11 #10179
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

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[max-sixty]

super, thank you @micguerr-bopen !

do you want to add a whatsnew? would be good to announce this to folks

lmk if you see anything in the docs that states what we support as a public API; then we could add this

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