Will allow importing the Protobuf without pulling in the rest of
the library. This is not a full PEP420 namespace, and the wheel still
bundles everything - it just makes things easier in a Bazel workspace.
I originally tried with PEP420, but it required more invasive changes,
and I ran into issues with mypy.
Disabled for now; when enabled it will allow faster collection
open and close in the normal case, while continuing to downgrade
when exporting or doing a full sync.
Also, when downgrading is disabled, the journal mode is no longer
changed back to delete.
