Add timeout-based subscriber receive

Add recv_timeout(Duration) to wait for a message until a timeout expires, so clients don’t need sleep loops or busy-waiting around try_recv().
Can follow the first version.

Support both typed and dynamic subscribers.

Start by locating the subscriber implementations and the existing try_recv() or first-version receive API. Add recv_timeout(Duration) for both typed and dynamic subscribers, then verify that each waits for a message until the timeout expires without requiring sleep loops or busy-waiting.

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