Missing types for `Comlink.finalizer` props on objects.

There is no TypeScript inference for the `Comlink.finalizer` prop, and it will always throw an error.

Additionally, it's not clear what a "exposed object" is, and on which end it should be called.

> If an exposed object has a property `[Comlink.finalizer]`, the property will be invoked as a function when the proxy is being released.