fix: initialize mqtt version from create options instead of assuming

[scootermon]

The following circumstances lead to an error when calling client.try_publish:

1. The client is configured to allow sending at any time.
2. The client is set up to use MQTTv5.
3. The client has not made an attempt to connect yet.

This fails because the Rust side doesn't know the correct MQTT version in this case. It assumes MQTT_VERSION_DEFAULT and ends up using the wrong callback fields when calling MQTTAsync_sendMessage. The C implementation catches this and returns a MQTTASYNC_BAD_MQTT_OPTION error.

I'm not sure if there's a good reason InnerAsyncClient assumes MQTT_VERSION_DEFAULT instead of copying the version from the create options, but as far I can tell that's the solution to this problem.

[fpagliughi]

Yeah, this sounds like a bug. I'll have a look at the PR shortly.