Wraps each v0.1 RPC, plus a WaitForHealth helper that polls until
the sidecar reports Ready=true (used at startup before any other
calls happen). Tests stub the gRPC server in-process so they don't
need a real sidecar JAR.
Real maestro driver will resolve selectors itself rather than
forcing the runner to look up coordinates from the hierarchy. Mock
now waits the requested duration so tests don't busy-spin and
starve the SDK fixture goroutine.
Records every call as an Action and lets tests program hierarchy,
screenshot, health, and per-method failures. Actions() returns a
copy so test code can't mutate the driver's history.
pj