when highestCpuUsage SystemRule is configured, the cpu usage become fluctuate widely

## Issue Description

#1050 deprecate bbr period of maxCpuUsage strategy, after that, the system cpu usage become less stable in second period level.
Since the CPU usage value held in `SystemStatusListener` updates every seconds, #1050 means that if CPU usage exceed threshold, all the traffic in next second will be blocked, and the cpu maybe fallen to an very low usage, so all the traffic in the second after next will pass, cpu usage back to a too high level, and so forth.

### Describe what happened (or what feature you want)

### Describe what you expected to happen

A relative steady cpu usage are expected when highestCpuUsage is configured.

### How to reproduce it (as minimally and precisely as possible)

### Tell us your environment

### Anything else we need to know?

Start by reading the highestCpuUsage SystemRule handling in SystemStatusListener and the changes from #1050. Reproduce the alternating CPU behavior with highestCpuUsage configured, then trace how the per-second CPU value controls traffic blocking. Done means the configured rule produces relatively steady CPU usage and the behavior is covered by a regression test.

Written by the indexing model from the issue text.