When you say
What do you mean? What message is the broker receiving? You can use something like MQTT Explorer to subscribe to all topics and ‘sniff’ your MQTT traffic.
You’ve got an error in your Item syntax - double colon ::
channel="mqtt:topic:mosquitto:ogFSmokeDetectorTopic::sensitivity
Depends. How is a self test executed via MQTT? If you only need this to be executed manually you might not need a rule.
As an aside, are you aware of the attribute option for zigbee2mqtt? Check this out to get rid of all your transforms: Zigbee2mqtt revisited: No more ugly transformations