Loose inferred return type of generator function

[purepear]

Description

The inferred type of the generator allows for extra properties(variant 1).
In the case of class extension it also requires narrowing the literal types(variant 3).
It seems to work well when the return type is set explicitly(variant 2, variant 4).

Looking at the source code(the generic types), I would expect the generator return type to be inferred properly 🤔

I'm not sure if this is a bug or a feature 😄

To Reproduce

https://stackblitz.com/edit/fishery-test?file=Post.ts

Additional context
Fishery version: 2.2.2