feat: add pure TypeScript Loro runtime

[zxch3n]

Summary

• add loro-js, a pure TypeScript Loro runtime with Text, Map, List, MovableList, Tree, Counter, events, undo, ephemeral state, JSONPath, and version transitions
• implement Rust-compatible update and snapshot codecs, generated interoperability fixtures, and Rust-to-TypeScript round-trip coverage
• add indexed sequence, ordered-state, style, deletion, and history paths so public operations match the Rust runtime's asymptotic behavior
• compress snapshot SSTables with interoperable LZ4, stream DeltaRLE decoding, and defer non-frontier history construction for initial snapshots
• document the current encoding format, runtime performance architecture, benchmarks, and publishing changesets

Why

Loro currently requires the WASM package for JavaScript consumers. This adds a portable TypeScript implementation while preserving the existing binary format and public behavior.

The initial implementation also exposed high-priority scaling failures: merged commits repeatedly copied and reduced complete history, concurrent Fugue insertion scanned growing origin chains, bulk List inserts emitted one operation per item, and large snapshots retained uncompressed or allocation-heavy intermediate data. This branch removes those paths and adds focused regressions.

Performance

Using zxch3n/crdt-benchmarks with the local build:

• B4: more than 180 seconds before the fixes, 2.846 seconds after them
• B3.5: 288 ms, versus 303 ms for the published Loro WASM adapter
• B3.3 snapshot: 240,032 bytes, down from about 7.95 MB and comparable to the WASM result
• 60k List and 120k Text updates now match the WASM adapter's encoded sizes

C1.1 remains a documented JavaScript representation and constant-factor gap rather than a known asymptotic regression.

Validation

• pnpm --dir loro-js check
• cargo test -p loro --test loro_js_interop
• pnpm --dir loro-js bench:complexity -- 1000,2000,4000,8000
• pnpm --dir loro-js bench:b4 -- 259778 3
• zxch3n/crdt-benchmarks B3.3, B3.5, B4, and C1.1 traces

[github-actions]

WASM Size Report

• Original size: 3053.22 KB
• Gzipped size: 1009.02 KB
• Brotli size: 707.57 KB