public void swapState(Routable rhs) {
        Object context = this.context;
        this.context = rhs.context;
        rhs.context = context;

        callStack.swap(rhs.getCallStack());
        trace.swap(rhs.getTrace());
    }
Swaps the state that makes this routable unique to another routable. The state is what identifies a routable for
message bus, so only one message can ever have the same state. This function must be called explicitly when
cloning and copying messages.

@param rhs The routable to swap state with.
messagebus/src/main/java/com/yahoo/messagebus/Routable.java