Periodically read cpuset categories until boot complete.

The cpuset categories are subject to change at any point during system
bootup, as determined by the init rules specified within the init.rc
files. Therefore, it's necessary to read the cpuset categories each
time before accessing CPU usage statistics until the system boot
completes. After boot complete, an external service may still cause
changes, which take a few seconds to propagate. Therefore, a delayed
task is initiated on boot completion to stop periodic reading and
ensure synchronization with the latest cpuset category updates.

Flag: EXEMPT fixing a minor bug
Change-Id: I260aab57c68fb1fa59bc1174613ce314d75baf7d
Test: atest CpuInfoReaderTest CpuMonitorServiceTest
Bug: 355099583