Fix nested optional row inference.

[robertwb]

This was broken in 2.40 and exposed by cross-langauge work.

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[robertwb]

R: @TheNeuralBit

[TheNeuralBit]

Note a user reported #22854 which was addressed in #22899. I'm not sure we need this patch, isn't it appropriate to create an Optional[RowTypeConstraint] for a nullable nested struct?

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[robertwb]

That is probably a better fix--didn't realize making it callable was all that was needed to make Optional[RowType] work.

[TheNeuralBit]

That is probably a better fix--didn't realize making it callable was all that was needed to make Optional[RowType] work.

Yeah for now it looks like CPython considers anything callable to be a type. In 3.11 it may become even more permissive: #22899 (comment)