Make AT specific targeting classes and fields optional

[srimanachanta]

Currently, fields like bestCamToTag and the entirety of the multitagResult are dependent on the pipeline settings and are wrapped by checks of their presence either by flags or by nullability. This is incorrect and should instead be replaced by using optional accessors to these values. This should also provide a small but decent speed increase the the serde Packet functions.

Diff can be copied from #1024 and #1058. Optional logic still needs to be implemented for PhotonTrackedTarget.