feat: add support for the "wsPreEncoded" writing option

A few notes:

- only the first element is pre-encoded, because the other elements are
buffers and will be sent as is over the WebSocket connection

- using `socket.packet()` was unexpectedly working, we will now use
`socket.client.writeToEngine()` (see [1])

See also: https://github.com/socketio/engine.io/commit/7706b123df914777d19c8179b45ab6932f82916c

[1]: https://github.com/socketio/socket.io/issues/3775