code: func NewClientHandler(tracer *zipkin.Tracer, options ...ClientOption) stats.Handler {
  	c := &clientHandler{
  		tracer: tracer,
  	}
  	for _, option := range options {
  		option(c)
  	}
  	return c
  }
docs: // NewClientHandler returns a stats.Handler which can be used with grpc.WithStatsHandler to add
  // tracing to a gRPC client. The gRPC method name is used as the span name and by default the only
  // tags are the gRPC status code if the call fails.