Make return type of `.create` methods more precise when passed shallowly loaded CoValues as inputs on fields

[aeplay]

[gdorsi]

Could you elaborate more on this one @aeplay?

[aeplay]

Could you elaborate more on this one @aeplay?

I.e. if I pass a shallowly loaded Pet to the create function of Person, the resulting person.pet should be equally shallowly loaded, type wise