Have you looked to tweak PSQL parameters to make it faster for test runs e.g. by disabling disk writes?
Regarding being language agnostic: YES, clients for languages other than go are very welcome. The integresql server actually provides a trivial RESTful JSON api and should be fairly easy to integrate with any language. This is our second iteration regarding this PostgreSQL test strategy, the last version came embedded with our legacy Node.js backend stack and wasn't able to handle tests in parallel, which became an additional hard requirement for us.
See our go-starter project for infos on how we are using integresql, e.g. our WithTestDatabase/WithTestServer utility function we use in all tests to "inject" the specific database: https://github.com/allaboutapps/go-starter/blob/master/inter...