feat(wasm): JSON text export of deep values

[zxch3n]

Stack: 4/6 — merge order: #1093 → #1085 → #1086 → #1087 → #1090 → #1091

Summary

Stacked on #1086 (which stacks on #1085); merge in order, GitHub retargets automatically.

Adds two bulk-read APIs on LoroDoc and every container class (LoroMap/LoroList/LoroMovableList/LoroTree/LoroText/LoroCounter):

• getDeepValueJson(): string — serde_json serialization of the deep value in ONE wasm call; same content as JSON.stringify(x.toJSON()).
• getDeepValueJsonWithIds(): { json: string, cids: ContainerID[] } — json is the deep value without ids; cids lists container ids in pre-order DFS of the serialized tree, so a consumer (e.g. loro-mirror) can re-attach ids in a single JS walk to reconstruct the getDeepValueWithID() shape.

The (json, cids) pair is produced by converting the with-id deep value to a serde_json::Value and stripping { cid, value } nodes in one pass, so cids order always matches the key/item order after JSON.parse, regardless of serde_json's preserve_order feature.

Benchmark (generated doc: 70,051 containers — Map 15,632 / List 9,956 / Text 44,463; 4.1 MB JSON; pnpm bench-deep-value-json)

Release build, median of 5 rounds:

case	time
toJSON()	75.6 ms
getDeepValueWithID()	137.0 ms
getDeepValueJson()	46.0 ms
getDeepValueJson() + JSON.parse	56.3 ms
getDeepValueJsonWithIds() + parse + re-attach walk	180.2 ms

The ≥5x target is not reachable: measured 2.4x end-to-end (getDeepValueJson()+JSON.parse vs getDeepValueWithID()). CPU profiling shows the bottleneck is the Rust-side deep-value walk + serialization (getDeepValueJson alone is 46 ms), not the boundary crossing — JSON.parse of 4.1 MB costs only ~5 ms. The JsValue structured-clone conversion accounts for ~75–80 ms of getDeepValueWithID()'s 137 ms. Dev (unoptimized wasm) build numbers: 370 ms → 280 ms (1.3x), dominated by dlmalloc/debug checks. Further wins would require reducing Rust-side materialization cost, not JS-side changes.

Caveats (documented in the changeset, doc comments, and context/wasm-bulk-read.md):

• Tree node meta maps serialize as plain deep values (matching getDeepValueWithID()), so meta container ids do not appear in cids.
• A plain object with exactly the keys cid + value where cid is a valid container id string is indistinguishable from a container node (inherent to the format).

Tests

• Rust: crates/loro-internal/tests/deep_value_json.rs (5 tests: content equality with plain deep value, exact pre-order cids, per-container variants, empty doc, detached errors).
• JS: tests/deep_value.test.ts extended (17 tests): JSON.parse(getDeepValueJson()) deep-equals toJSON() for doc + all 6 container types; re-attach walk reconstructs getDeepValueWithID() exactly.
• Full wasm suite: 27 files / 366 tests pass; tsc --noEmit clean; cargo test -p loro-internal / -p loro pass.

Wasm binary size

Dev build with debug info: +524 KB (+0.52%) vs the parent branch.

[github-actions]

WASM Size Report

• Original size: 3139.98 KB
• Gzipped size: 1040.15 KB
• Brotli size: 729.47 KB