Builds on top of #17659
Move the filesystem + sqlite thread listing-related operations inside of
a local ThreadStore implementation and call ThreadStore from the places
that used to perform these filesystem/sqlite operations.
This is the first of a series of PRs that will implement the rest of the
local ThreadStore.
Testing:
- added unit tests for the thread store implementation
- adjusted some unit tests in the realtime + personality packages whose
callsites changed. Specifically I'm trying to hide ThreadMetadata inside
of the local implementation and make ThreadMetadata a sqlite
implementation detail concern rather than a public interface, preferring
the more generate StoredThread interface instead
- added a corner case test for the personality migration package that
wasn't covered by the existing test suite
- adjust the behavior of searched thread listing to run the existing
local rollout repair/backfill pass _before_ querying SQLite results, so
callers using ThreadStore::list_threads do not miss matches after a
partial metadata warm-up
Introduce a ThreadStore interface for mediating access to the filesystem
(rollout jsonl files + sqlite db) based thread storage.
In later PRs we'll move the existing fs code behind a "local"
implementation of this ThreadStore interface.
This PR should be a no-op behaviorally, it only introduces the
interface.
