Function handle_watch 

pub async fn handle_watch(
    server: &ProtocolServer,
    req: WatchRequest,
    tx: Sender<Result<WatchEvent, Status>>,
)

Long-running handler for the WATCH server-streaming RPC.

Subscribes to the shared [EventBus] and forwards every event to the client via the provided mpsc::Sender. The loop terminates when:

• The client disconnects (send fails).
• The event bus is dropped (channel closed).

Lagged receivers (slow consumers) log a warning and continue.