types(model+query): unpack arrays in distinct return type

[vkarpov15]

Fix #14026

Summary

Unpack<T> returns the array element type if T is an array, or T otherwise. We already use Unpacked<> in some similar cases, like async iterators for aggregate().

Examples

[hasezoey]

Looks good, to my understanding this should also change if the inferred type is used, maybe add a test for that too? (no explicit interface)