DM-8097 uncovered a problem with raw_sub in the butler that resulted in some fixes in DM-13696 but left the underlying problem remaining because raw in obs_base was still defined as a DecoratedImageU.
In this ticket I will:
- Change raw to ExposureU (which is more inline with other obs packages).
- Re-enable the test for raw_sub (and fix it)
- Update obs_test test to expect ExposureU
- Fix obs_lsst raw_sub now that the test it uses from obs_base will be enabled.