Direct transports don't respect roundrobin and prefetch settings

Instead just sends messages as fast as it can. Some projects rely on these to work, either because they can't handle concurrency (`prefetch: 1`) or just need to limit to not cause thrashing with hundreds of concurrent jobs.
Currently these can't use/test with `direct://`, and typically have to use AQMP always. Which is inconvenient for tiny installations and/or tests.

Also goes for MQTT.
