0.13.1

This release matches HarfBuzz v14.3.1, and has an MSRV (minimum supported Rust version) of 1.85.

• Saturate shaping and positioning math across GPOS, kerx, trak, fallback,
  shaping, metrics, and font scaling paths to avoid overflow and better match
  HarfBuzz behavior (#420).
• Cache GDEF mark filtering sets in bitmaps (#421).
• Lock icu_properties to 2.2.0 (#422).
• Optimize hot loops in contextual and layout matching by probing rules before
  parsing, hoisting invariants, moving recursion state instead of cloning, and
  replacing per-element copies with block copies (#423, #424, #425).
• Optimize buffer internals by copying small counts inline and charging
  move_to operations against max_ops (#426, #429).
• Improve AAT shaping performance by walking morx subtables through packed
  descriptors, resolving subtable kinds from cached parts, and adding a
  state-machine fast path (#428, #430, #431).
• Skip the post-morx digest update when GPOS is not present (#433).
• Add a batched nominal-glyph callback to FontFuncs (#434).
• Update read-fonts to 0.43.2 (#432, #435).