Duality Serializers should support updating an existing instance when loading

[ilexp]

Summary

Right now, Duality serializers always return a new instance of a deserialized / loaded object. This should be extended to allow updating an existing instance.

Analysis

• Deep instance re-use would be the ideal case, but will need further investigation.
• Shallow instance re-use for only the provided top-level object could be some first iteration middle ground, but should only be done if significantly easier than the deep case, depending on investigation results.
• A workaround in the mean time could be to deserialize into a new temp instance and use the cloning system to copy all values over to the existing instance.