docs: public static StatsTraceContext newServerContext(
        List<? extends ServerStreamTracer.Factory> factories,
        String fullMethodName,
        Metadata headers) {
      if (factories.isEmpty()) {
        return NOOP;
      }
      StreamTracer[] tracers = new StreamTracer[factories.size()];
      for (int i = 0; i < tracers.length; i++) {
        tracers[i] = factories.get(i).newServerStreamTracer(fullMethodName, headers);
      }
      return new StatsTraceContext(tracers);
    }