Modern Serialization of Custom Datatypes

From #443, encoders/decoders are used to handle serialization of fields with datatypes like np.ndarray and torch.Tensor. This is not longer well supported in pydantic V2. I am guessing we could modernize by using @field_serializer for much of this or wrapping the array objects.

I have a custom implementation of serialization + compression in apsopt (ala b64zstd:(encoded array data)), will try port over as custom serializers.