DurableObject type should work in the mixin case

[supfilistine]

Typescript offers a wonderful way of mixing in classes in order to get beyond the limitation of being able to extend only one class in JS.

ts-mixer is a great project and I checked it works with abstract classes, which Rpc.DurableObject is. I am not sure why then it doesn't detect that my DO class is extending it, just not in a conventional way.

Does anything jump out at you when you look at the example code I shared in this issue?