This refactors the PDS to use a single-tenant SQLite datastore.
Each user has their own SQLite file that stores their repo and private account state.
User databases are stored hierarchically as such: /${dbDirectory}/${sha256Hex(did).slice(0,2)}/${did}
Repo signing keys for each repo are stored alongside the SQLite file.
We also switch out the abstraction for interacting with user data to an ActorStore
. The primary difference be