Expose WaitUntilReady constructors

I'd like to add a custom check, a real connection to the database with a test query. Something like this:

mariaDBReady :: TestDBInfo -> WaitUntilReady
mariaDBReady db = WaitReady $ \container -> do
    withFrozenCallStack $ do
        let (endpointHost, endpointPort) = containerAddress container db.dbPort
            ci =
                defaultConnectInfo
                    { connectHost = unpack endpointHost
                    , connectPort = fromIntegral endpointPort
                    , connectUser = unpack db.dbUsername
                    , connectPassword = unpack db.dbPassword
                    , connectDatabase = unpack db.dbName
                    }
            wait = do
                r <- try (connect ci >>= flip query_ "select 2 + 3")
                case r of
                    Right [Only (i :: Int)] -> do
                        pure ()
                    Left (ex :: IOException) -> do
                        threadDelay 500000
                        wait
        liftIO wait

This is currently not possible since WaitReady is not public.

Start by locating the WaitReady constructor and the module export list that currently keeps it private. Check how existing readiness checks are represented, then expose the constructor so callers can define custom database checks like the example. Confirm that the public API still builds and that a custom WaitUntilReady value can be constructed.