code: func (g *Group) setEvaluationTimestamp(ts time.Time) {
  	g.metrics.groupLastEvalTime.WithLabelValues(groupKey(g.file, g.name)).Set(float64(ts.UnixNano()) / 1e9)
  
  	g.mtx.Lock()
  	defer g.mtx.Unlock()
  	g.evaluationTimestamp = ts
  }
docs: // setEvaluationTimestamp updates evaluationTimestamp to the timestamp of when the rule group was last evaluated.