Review metadata layout for data/storage and file objects

Core structures already in place in 0.2 beta 1 (part/snap/delta for data, incarnation/copy) for storage.

- Review structures and naming.
- Confirm physical storage definition also works for FILE objects
- Review Python domain code gen to make sure nothing else is needed for these structures

Start by locating the metadata definitions for part, snap, delta, incarnation, and copy, then inspect the Python domain code generator that handles them. Review the structures and naming, verify that the physical storage definition also covers FILE objects, and confirm the generated domain code needs no additional changes.

Written by the indexing model from the issue text.