Default numbers don't fit in cells

[luke-quadratic]

[davidfig]

This is a bit complicated. We'll have to move the number rendering (ie, determining what the string of the number looks like from its options and values) from Rust to TS, since we'll need to adjust how it's displayed based on its actual rendering size, which we can only calculate while rendering.

I started prototyping this work, but I'd rather wait until #1406 (vertical wrapping) is merged, as I'l touch similar files to that one.