[FEATURE REQUEST] Allow sending Streams and Futures as input to Isolate

[lohnn]

Is your feature request related to a problem? Please describe.
It is now impossible to send Futures and Streams as input to a StatefulIsolate, allowing this would greatly increase usability.

Describe the solution you'd like
StatefulIsolate should be able to handle such cases and send the items one by one to the isolate with a protocol specifically for supporting this use case. (Basically same as for Isolate -> Main, but the other way).

The backpressure strategy should consider a full stream as one input and not handle the stream as individual items/jobs.

Describe alternatives you've considered
The workaround is to await the value/values and send them manually, but that might yield unexpected results depending on backpressure strategy.