Grapheme cluster break algorithm sometimes produces wrong results.

[JosepMariaBlasco]

For example, नमस्ते is broken as 4 clusters (should be 3).

[JosepMariaBlasco]

It's more complicated than I thought. This might not be a bug: "Grapheme clusters may contain several base-level units, but up to Unicode 15 always broke after virama characters". See https://www.unicode.org/L2/L2023/23140-graphemes-expectations.pdf