FindFreePort returns an available port that can be used for a server.

StartDuckSqlServer starts a sql-server on a free port from the specified directory |dir|.

StopDuckSqlServer stops the running Dolt sql-server.

WaitForSqlServerToStart polls the specified database to wait for it to become available, pausing between retry attempts, and returning an error if it is not able to verify that the database is available.

Create a struct that stores all these values:.