The median username length is 8 characters. The 99% percentile is 18
characters. The 99.9% percentile is 24 characters. About 750 users have
a name more than 24 characters long.
This doesn't do anything about existing users with long usernames.
Note that this is the length in Unicode codepoints, not grapheme
clusters. Some Unicode characters and emoji may be a single glyph but
composed of multiple codepoints.
