ruff_linter: fix handling of unprintable characters
Previously, we were replacing unprintable ASCII characters with a
printable representation of them via fancier Unicode characters. Since
`annotate-snippets` used to use codepoint offsets, this didn't make our
ranges incorrect: we swapped one codepoint for another.
But now, with the `annotate-snippets` upgrade, we use byte offsets
(which is IMO the correct choice). However, this means our ranges can be
thrown off since an ASCII codepoint is always one byte and a non-ASCII
codepoint is always more than one byte.
Instead of tweaking the `ShowNonprinting` trait and making it more
complicated (which is used in places other than this diagnostic
rendering it seems), we instead change `replace_whitespace` to handle
non-printable characters. This works out because `replace_whitespace`
was already updating the annotation range to account for the tab
replacement. We copy that approach for unprintable characters.
