PostgreSQL data source, built on Lotus.Source.Adapters.Ecto.
Resolved automatically for any repo whose Ecto adapter is
Ecto.Adapters.Postgres, so hosts normally never name this module —
they configure the repo and Lotus wraps it.
Dialect behaviour comes from
Lotus.Source.Adapters.Ecto.Dialects.Postgres: schemas, EXPLAIN (FORMAT JSON) query plans, a session search_path, and statement_timeout.