Function call_rpc 

pub async fn call_rpc<C, P, R>(
    ctx: AppContext,
    client: C,
    params: P,
    rpc_call: impl FnOnce(C, Request<P>) -> Pin<Box<dyn Future<Output = Result<Response<R>, Status>> + Send + 'static>> + Send + 'static,
) -> Result<Response<R>, Status>
where
    C: Clone + Send + 'static,
    P: Send + 'static,
    R: Send + 'static,