Make all entrypoint stream compatible

[conico974]

All entrypoint should be stream compatible both for the input and the output.

• Create an internal interface that all entry will follow. All accepting a ReadableStream body and additional value as serializable data
• Make the InternalEvent body a ReadableStream
• Make StreamCreator effectively mandatory (The stream can perfectly be empty)
• Maybe rethink the role of converters
  Some wrapper will likely never use the streams, but it will help having a single interface.