z.ws:f
Where f is a unary function, it is evaluated on a message arriving at a websocket. If the incoming
message is a text message the argument is a string; if a binary message, a byte vector.
Sending a websocket message is limited to async messages only (sync is 'nyi). A string will be sent as a
text message; a byte vector as a binary message.
The default definition is to echo the message back to the client, i.e. {neg[.z.w]x}