MySQL data source, built on Lotus.Source.Adapters.Ecto.
Resolved automatically for any repo whose Ecto adapter is
Ecto.Adapters.MyXQL, so hosts normally never name this module —
they configure the repo and Lotus wraps it.
Dialect behaviour comes from
Lotus.Source.Adapters.Ecto.Dialects.MySQL: databases-as-schemas, EXPLAIN FORMAT=JSON query plans, and max_execution_time as the statement timeout.