psh_utils: Internally cache power stats

To avoid frequent (expensive) collection of power stats
allow the use of cached values with a certain time
tolerance.

Flag: com.android.media.audioserver.power_stats
Test: atest powerstats_collector_tests
Test: atest audio_powerstatscollector_benchmark
Bug: 350114693
Change-Id: I952950e5373e3c4b8ebc765bf6fb2cf8def0962e