Optimize job setTimer

[fufuok]

What does this do?

One more optimization:

When NTP time is calibrated or a leap second occurs, the following conditions may occur:

Now: 2022-01-01T00:00:00Z
Job:
nextRun.duration = 2*time.Mintue,
nextRun.dateTime = 2022-01-01T00:02:00Z

//...

Now: 2022-01-01T00:02:00Z
// ntpdate
// system time is corrected
Now: 2022-01-01T00:01:58Z

job.setTimer(time.AfterFunc(next.duration, func() {
	if !next.dateTime.IsZero() {
		for {
			if s.now().Unix() >= next.dateTime.Unix() {
				break
			}
			// ...will loop for 2 seconds
		}
	}
	s.runContinuous(job)
}))

This should be better:

job.setTimer(time.AfterFunc(next.duration, func() {
	if !next.dateTime.IsZero() {
		for {
			n := s.now().UnixNano() - next.dateTime.UnixNano()
			if n >= 0 {
				break
			}
			s.time.Sleep(time.Duration(n))
		}
	}
	s.runContinuous(job)
}))

Which issue(s) does this PR fix/relate to?

List any changes that modify/break current functionality

Have you included tests for your changes?

Did you document any new/modified functionality?

• Updated example_test.go
• Updated README.md

Notes

[JohnRoesler]

nice, thank you!