Exclude IOWAIT from CPU stats

[ThatOneCalculator]

Ref: https://git.joinfirefish.org/firefish/firefish/-/issues/10755

From our issue tracker:

What feature would you like implemented? (Please give us a brief description of what you'd like.)

Excluding IOWAIT from the CPU usage widget.

Why should we add this feature? (Please give us a brief description of why your feature is important.)

Counting IOWAIT in CPU usage can give an inaccurate representation of actual CPU load, since the CPU is idle during IOWAIT and can still process other things.