Update internal Cosmos provider code for NRTs

[ajcvickers]

For example, some properties of SelectExpression in the Cosmos provider are marked as non-nullable, but are used as nullable in the code:

• Limit
• Offset
• Predicate

[roji]

IIRC most of Cosmos query internals isn't NRT-annotated (there's lots of #nullable disable there) because it's going to be redone anyway... /cc @smitpatel

[ajcvickers]

@roji Is this tracked somewhere?