Add a combined worker-and-client test helper to `TemporalTestServer`

[RalucaP]

Integration tests require nesting withConnectedWorker and withConnectedClient plus creating a TemporalWorker.Configuration by hand every time. A single withWorkerAndClient on TemporalTestServer would cover the common case and match what the SDK's own tests already do internally.

Ref: #141 (comment)