generic mixin type

[obriencj]

I'd like to figure out how to enable a generic inheritance that does the same thing proxytype does. Even better if we could make it safe for runtime.

class SomeClass(VirtualMixin[ClassA, ClassB, ClassC]):
    ...

Would be similar to a proxytype definition to mix the definitions of ClassA, ClassB, and ClassC into the SomeClass definition.

In addition, I'd really love dynamic mixin casting,

class SomeClass(VirtualMixin):
    ...

val: SomeClass[ClassA, ClassC] = get_some_class()

This would be useful for situations where the union of mixins is dynamic locally, but somewhat fixed locally. For example, you're connecting to a koji instance with a few known plugins enabled which add new hub API calls. Those plugins could be defined in separate protocol definitions.