fix(graphical): fix nested error wrapping

[TheLostLambda]

Fixes #333

Here is an error now nicely wrapping (with the 2 char padding on either side) of a 50-char wide terminal:

[TheLostLambda]

There is a second error here too that's come up! The prefixes for #[related] errors are messing up the line-width calculations:

The easiest solution seems to be changing the header to always add a newline after one of these tags — something that I think looks nicer anyways!

I'll also include that change in this PR!

[TheLostLambda]

I've also fixed the spacing around / between related errors, and I'm trying to fix up some unrelated CI breakage (the new nightly compiler seems to be much better at / to much more aggressively detect dead code!)

[TheLostLambda]

Oof, lots of little things making that slightly tricky, but ready for review now! I tried to keep some nice and meaningful commits if you're the type of person to review those diffs one-at-a-time!

[TheLostLambda]

Finally, if you're looking for more example outputs and how they have changed / been restyled, here are plenty more examples: TheLostLambda/pgfinder-next@23a4093

[zkat]

Thanks for taking care of this! this looks a lot better :)