Improve number reporting in `add_categorical_bound_constraint`

[jonashaag]

I'm getting constraint failure messages like

6.288887928086567e-05% (20 out of 31802125)

and

1.0073226238812658% (320350 out of 31802125)

In both cases, using fewer decimal places would be nice I think. At the very least we shouldn't be showing scientific notation + % IMO.

For the counts, I think it would be nice to display them like Python does, ie. 320_350 out of 31_802_125.

[jonashaag]

Also, are we giving the numbers in % here or in fraction? To me it looks like the distribution and default_bounds argument are in [0, 1] but the reported numbers are in [0, 100]...

[0xbe7a]

The parameters are in [0, 1] and the reported numbers are in [0, 100]. The reporting issue does not only exist here and we are working on fix, see #89