feature: Mashal/Unmarshal having only a parametrized interface #563

Is your feature request related to a problem? Please describe.

I have interfaces like this:

type Scalar[T any] interface {
    Add(rhs Scalar[T]) T
}

I want to directly marshal and unmarshal having only the interface itself. If this interface wasn't parametrized, then I could have defined an encoder/decoder with a TagSet where I would add the concrete types of Scalar. I can't do that when the interface (and by extension, the concrete type that's implementing it) is parametrized as I have to fill out the concrete type's parameters at TagSet.Add time without knowing what they are.

Describe the solution you'd like
To directly marshal an unmarshal, having only the parametrized interface itself.

Describe alternatives you've considered
N/A

Additional context
N/A