Make EventBus types a little bit more strict

[ghost23]

Hi,

consider this little code example:

type MyCallbacks = {
  'MyEvent': (someParam: boolean) => void;
};

const myEventBus: EventBus<MyCallbacks> = new EventBus();

This currently does not lead to an error, but I think it would be nice, if it did.
Because currently I have no way of enforcing an eventBus to support a specific set of typed events, because you can always simply assign any EventBus instance to any eventBus variable.

And by the way, this also does not lead to an error:

type MyCallbacks = {
  'MyEvent': (someParam: boolean) => void;
};

type MyOtherCallbacks = {
  'MyOtherEvent': (otherParam: number) => void;
};

const myEventBus: EventBus<MyCallbacks> = new EventBus<MyOtherCallbacks>();

I believe the way this could be fixed would be to simply change the Typescript definition for the EventBus class as follows:

export class EventBus<in out T extends Callbacks = Callbacks> {
   // rest stays the same
}

Notice the "in out" that has been added, which sets the variance of the generic class specifically to invariant. This needs Typescript 4.7 or higher.