docs: public static ZContext shadow(ZContext ctx)
      {
          ZContext context = new ZContext(ctx.context, false, ctx.ioThreads);
          context.linger = ctx.linger;
          context.sndhwm = ctx.sndhwm;
          context.rcvhwm = ctx.rcvhwm;
          context.pipehwm = ctx.pipehwm;
          return context;
      }