xmrig's RandomX pollutes the L3 cache, making other processes appear
~3-8% busier. With a single 5% threshold for both stopping and
resuming, the script oscillates: start xmrig -> cache pressure
inflates CPU -> stop xmrig -> CPU drops -> restart -> repeat.
Split into CPU_STOP_THRESHOLD (15%) and CPU_RESUME_THRESHOLD (5%).
The stop threshold sits above xmrig's indirect pressure, so only
genuine workloads trigger a pause. The resume threshold confirms the
system is truly idle before restarting.