Prototype an approach to the "versioned cameras" concept that allows camera definitions and datasets to be unversioned (representing a "nominal camera"), with all versioned quantities stored in IsrCalib objects in data repositories; that versioned content will be added to the Camera object on read via new factory classes/methods.

This ticket is prep work for an RFC on the topic, which will include much more detail on the plan and philosophy; I just want to work through some open questions by trying to code pieces of them first.