Merge branch 'ps/odb-generalize-prepare'

The 'reprepare()' callback for object database sources has been generalized into a 'prepare()' callback with an optional flush cache flag, and a new 'odb_prepare()' wrapper has been introduced to allow pre-opening object database sources. * ps/odb-generalize-prepare: odb: introduce `odb_prepare()` odb/source: generalize `reprepare()` callback