- Extract shared namespace for looking up and hashing keys
- Require storage transformers only to implement a loader that
associates known keys with metadata
- Move key loader/lookup utils to utils directory to avoid
multiple "storage" packages in imports
libraries/shared; adjust omni test_helpers to drop and recreate
checked_headers table to avoid reaching 1600 column limit after repeated
tests (dropping columns doesn't actually remove them from contributing
to that limit)