fix(rust): simplify new function optional logic

[ctrlaltf24]

Used to be a code path (where isFreeFormObject and something else) where we could end up with two : None : None's. (See the added test for how to reproduce the failure)

This does add the None for the !required && !isArray && !isMap && !isNullable case (where nothing would have been printed before.

Above for the type on the individual vars inside the struct definition the logic is simply if not required then it's optional. If it's optional we want a None when creating a new struct.

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