To be able to capture+encode needed information in the purl to/from claircore.Package transformation that "SBoM support" necessitates, we're going to need to be able to make changes to the latter (and the corresponding database backing).

Currently, the claircore types are used directly in the clair HTTP API, making this hard. They should be split apart so that we can make claircore changes without unintended changes in clair.