use average of (1 - CPU idle ratio) across CPUs in the cluster for P- and E-Cluster usage

[ericcanton]

Fixes #59

I'm not sure this is equivalent to the previous value, but it works as expected with and without load on the CPU.

Verified to work on M3 macbook.

[ivanfioravanti]

Confirmed it works on M3, please merge it 🙏

[techyogi]

confirmed working.

[Vlor999]

Hi everyone, since this project seems to be unmaintained and has accumulating bugs with recent macOS updates, I've created an actively maintained fork called mxtop. It includes pending community fixes and is fully working on the latest Apple Silicon chips.
You can install it right now using: pip install mxtop The new repository is here: https://github.com/Vlor999/mxtop
Feel free to open issues or PRs there!