Higher cpu usage precision

[flipflop133]

Currently, BPYTOP only display CPU usage with one decimal place (e.g. 2.3%), it could be great to be able to set the precision in the config file to get something more like (2.325%), to help diagnostic small background scripts.

[adavidzh]

bpytop presently uses 4 characters to display this information: NN.N (%).

Related, I would argue that it would make sense to try and keep the number of significant digits constant and use something like:

[99.9 ]
[73.5 ]
[ 0.05]

I added the [] for clarity and note that it is not 99.90 or 00.05.

This could be done along with the ability to parameterise via configuration.