Fixed OTSubscriberEventHandlers type for connected member

[gguidotti]

This PR fixes an incorrect type for the connected event in OTSubscriberEventHandlers.
Given the following code:

const subscriberEventHandlers: OTSubscriberEventHandlers = useMemo(
  () => ({
    connected: (event) => {
      console.log('connected', event)
    }
  }),
  []
)

TypeScript throws the warning: Parameter 'event' implicitly has an 'any' type.

However, when logging the event, I noticed that it adheres to the Stream type. I've updated the library types accordingly to eliminate the warning.
I suspect the same applies to the disconnected event, but since I couldn't see it fire in my code I haven't updated it (I wasn't sure about the type for this event).