FR: Proportional font, to fit more text in horizontal space

Hi there, Aside: I like Speedscope, I'm particularly impressed by the effort you've put into supporting so many output formats. I'm trying to [map the profiler ecosystem](https://www.markhansen.co.nz/profilerpedia/) and Speedscope is one of the most-connected profiler UIs I've found -- bravo!.

I have a suggestion: try a proportional font, rather than a fixed-width font, for the stack frames in the Time Order and Left Heavy views. In these views the horizontal space is constrained and expensive. A proportional font would let you show more information to users in the same space.

I understand there's a cool coder aesthetic to the monospace font, but I think proportional fonts, at least in the graphs, could be a really big usability win to increase the information density.

Thanks for your consideration,
Mark