Use `cpupower` tool instead of custom implementation

[smarr]

See

• https://wiki.archlinux.org/title/CPU_frequency_scaling#Scaling_governors
• and it's in the linux-tools-common package on Ubuntu: https://packages.ubuntu.com/search?searchon=contents&keywords=cpupower&mode=exactfilename&suite=noble&arch=any

[smarr]

Don't forget to check #140

It already references https://pyperf.readthedocs.io/en/latest/system.html