Add network debugging (network:* messages)

[ERnsTL]

• these are the messages

  • network:connect
  • network:begingroup
  • network:data
  • network:endgroup
  • network:disconnect

• They are activated using network:edges.

• TODO how to intercept data to/from a direct process-to-process ringbuffer/channel?

  • does it make sense if the processes decide themselves what they send for debugging? Otherwise we would have to wrap channel.pop() into a flowd.receive() method, which checks network debug mode for every IP transfer and checks for the edge being selected for debugging, and then makes a copy to be sent as network:data output message
  • but maybe that would be good anyway in order to create encapsulation (hide rtrb, npnc, mpsc channel etc. implementation)