Toolchain refresh; API (encode/decode/dumps/loads) unchanged. See
"Migrating from 1.x" in the README.

- TypeScript 3.7 -> 6.0, ESM-only, NodeNext.
- jest@24 + ts-jest + ts-node + yarn -> bun (install, test, dev).
  41 jest tests ported to bun:test, all pass.
- Drop the private:true + dist-extras.ts publish-from-dist machinery;
  standard files glob now controls what ships.
- Python parity tests moved to legacy-python-tests/ with a manual-run
  README (brittle CI surface for marginal value over the unit tests).
- Publish via npm Trusted Publishing on tag push (no NPM_TOKEN).
- Requires Node 22+ / Bun 1.2+.