Use monospaced font for numbers

[parttimenerd]

Consider the case of two numbers which are shown in the call tree table:

This invalidates the common notion that wider numbers are larger. A simple fix could be to use font-family: monospaced:

[mstange]

We should use font-variant-numeric: tabular-nums for these.

[parttimenerd]

It looks like

I'll add a small PR tomorrow.