Decode does not process pointer elements

[jpswinski]

In the SlideRule record definitions, if a field is marked as a pointer, then it is passed over by the __decode function in the Python client.

https://github.com/ICESat2-SlideRule/sliderule-python/blob/ed9a90b028142126b8aed6037399cbcdaf83a359/sliderule/sliderule.py#L176-L178

The client needs to be updated to support pointers - this will allow variable length rich data structures to be passed from the server to the client. Currently, the only support for variable length rich data structures is to have up to one array of them at the end of the record.

[jpswinski]

This requires some way of representing the RecordObject pointers when de/serialization happens.