Function send_operator_terminal 

async fn send_operator_terminal(
    tx: &Sender<Result<RtdlEvent, Status>>,
    node: &NodeEventContext,
    state: u32,
    reason: &str,
    runtime: &PlanRuntime,
)

Stream the terminal event for a non-leaf RTDL operator node, and record the state so get_plan_status reflects it.