Default implementation of :communication_module.

Essentially cast/2 behaves as :gen_statem.cast/2 and reply/2 behaves as :gen_statem.reply/2.

This is introduced in order to work-around slow message passing to unreachable nodes; if the target node is not connected to Node.self(), functions in this node give up delivering message. In order to recover from temporary network issues, reconnecting to disconnected nodes should be tried elsewhere. Note that :raft_fleet (since 0.5.0) periodically tries to re-establish inter-node connections out of the box.