Move callback back to main isolate

Currently, the end-developer has to take care of isolate communication themselves.
That's not really necessary, as all the parameters of the callback can be sent from one isolate to another.
It would make the developer experience much nicer if the library took care of sending these data across isolates and just have a set of callbacks on the main isolate waiting which are called with the appropriate parameters whenever an update arrives.

No files or tests are identified in the issue. Start by locating the plugin's isolate communication and callback entry points, then verify how callback parameters are transferred; done means the library forwards updates to callbacks on the main isolate without end-developer-managed communication.

Written by the indexing model from the issue text.