Script-range boundaries alone don't bound group size — dense Unicode
blocks (CJK, user fonts) can produce groups of hundreds of KB. Add a
64 KB hard cap: when adding the next glyph would exceed it, close the
current group and start a new one with the same script ID.
64 KB is well above the largest current built-in group (~50 KB for
notosans_18 Cyrillic) and a safe transient malloc on the ESP32-C3.
The decompressor side already handles any number of groups per font.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
