Add Packing options to PredictionRigidbody

[AustinEast]

Im running into issues with accuracy when reconciling my Predicted Rigidbodies, and I've narrowed it down to the RigidbodyState reconciling with a packed Quaternion - after manually updating the RigidBodyState writer/reader to use unpacked quaternions my issues are resolved.

So my request would either be to add an option to set the Packing on the PredictionRigidbody/RigidbodyState, or to expose the internal PredictionRigidbody.SetReconcileData() method so that we can easily write our own writers/readers for the type (the mentioned internal method is the main blocker for this DIY approach).