Local Pairing - Change Messenger sync behaviour based on state

[Samyoul]

I notice is that a lot of the syncing methods now have a nilable parameter, that seems to be nil in the majority of cases. Perhaps we could simplify the method logic and update Messenger's state with a "RawMessageHandler" register.

The consuming code would look like something below:

m.SetRawMessageHandler(rawMessageHandler)
m.SyncDevices()
m.SendPairInstallation(context.TODO)
m.ResetRawMessageHandler() // Defaults back to `dispatchPairInstallationMessage()`

Implementing this change would simplify the calling of all the functions that have an optional RawMessageHandler , future developers don't need to know what a RawMessageHandler is unless they want to change "broadcasting" behaviour.

---

Additionally we have precedent for altering Messenger behaviour via an update to state with the use of the localPairing field, this is used as below:

func (m *Messenger) hasPairedDevices() bool {
	logger := m.logger.Named("hasPairedDevices")

	if m.localPairing {
		return true
	}

	...
}

Consider the relationship between these two factors, localPairing and RawMessageHandler. Is there a link between them that would affect the implementation?

Perhaps if localPairing is true, a non-default RawMessageHandler should be present?

Details

#3202 (comment)