implement Wrapped interface to expose EventLoop scheduler for r2dbc-pool optimization

When r2dbc-pool can access the connection's EventLoop scheduler via unwrap(Scheduler.class), it can schedule connection acquisition operations directly on the connection's event loop, reducing thread context switching and improving overall throughput.

this requires the client interface to add getScheduler() method to expose the EventLoop
and implement Wrapped<Object> interface with unwrap(Scheduler.class) support