v2.12.0

• Unicode 18 support (#354). (This includes the modified grapheme-break rule
  GB9c in UAX 29, which removes some grapheme breaks for Indic characters.)

• options arguments are changed from an enum to unsigned int, since
  they are generally bitwise "or" of enum values; this should be backwards
  binary compatible (#353).

• int *last_boundclass parameter of utf8proc_decompose_char is changed to
  a utf8proc_int32_t * (affecting only rare systems where int is not 32 bits, on
  which the last_boundclass argument would have produced incorrect results) (#363).

• New utf8proc_free function to free memory allocated by utf8proc (#338).
  (You can also use your own memory allocator by calling lower-level APIs.)

• utf8proc_normalize_utf32 can now handle invalid codepoints ≥ 0x110000.
  They are passed through unchanged rather than dropped, and composition never
  runs across one (#352, #355).

• Fix UTF8PROC_CHARBOUND emitting no 0xff grapheme markers when combined
  with UTF8PROC_COMPOSE or UTF8PROC_DECOMPOSE, a regression in 2.11.3
  (#355).

• Zig build scripts (#351).

• Minor build-system improvements (#326, #327, #334).