feat: add TypeScript fractional index package (#979)

* feat: add TypeScript fractional index package

* fix: prevent fractional index byte aliasing

* fix: handle zero-prefixed fractional indexes

* refactor: expose fractional indexes as strings

* ci: install fractional index test deps

* chore: use Vite+ tooling for fractional index

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Co-authored-by: Zixuan Chen <zx@loro.dev>