Detect closed connections and automatically attempt to reconnect them.

[lmwnshn]

The Worker creates a connection here in its constructor.

However, if the connection is closed by the DBMS (e.g., hammer a CPU-limited PostgreSQL read replica with reads to the point of replication replay being blocked), the Worker does not recover and tries to execute on the closed connection.

We would like the closed connection to be reopened. Maybe add a setting for whether this behavior should happen.