Merge branch 'ps/odb-generalize-prepare' into next

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