This struct exists exclusively for serializing State’s to disk without
including all_bytes. If more entries end up in State that need to be
saved off, change this struct to reflect them.
When printing [1, 2, 3, 4, 5, 6, 7] on a width of 3, the
maximum 0-up line number is 3. This function returns that
calculation. See test_max_bytes_line for examples
.len gives the number of bytes
.chars.count() gives the number of characters (which counts è as two characters.
The human concept is unicode “graphemes” or “glyphs” defined to be what
think they are.