do not re-create UnixStream on every message

[jonniek]

unix socket throws some errors because we are not keeping the socket open to listen to responses

[ipc_8] Write error (Broken pipe)

It would be more efficient not to open the socket on every message too.

The open socket could be put in app state in a Mutex, but that makes it messy to avoid in windows with cfg flags. Maybe there is something more elegant.