rules/manager.go
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
}
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
}
// setEvaluationTimestamp updates evaluationTimestamp to the timestamp of when the rule group was last evaluated.