Reduce text insert and import overhead

[zxch3n]

Summary

• avoid duplicate text insert boundary validation and add a fast path for coordinate systems where every text position is already a valid boundary
• skip eager imported change block validation during snapshot/update import
• make lazy external change block decode paths return failure instead of panicking when malformed blocks are encountered
• fix a default-feature compile error in an arena test and sync Cargo.lock for the current loro-wasm version

Rationale

Text insert was paying boundary validation costs twice on the attached path, and ASCII style workloads could avoid the expensive conversion round trip entirely. Snapshot import was also parsing every imported change block immediately via validate_imported_change_blocks even though the import blob and sstable layers already verify checksums. This keeps import on the lazy path while preserving non-panic behavior if a malformed block is encountered later.

Validation

• cargo check -p loro-internal
• cargo test -p loro-internal import_rejects
• cargo test -p loro-internal --test test test_from_snapshot
• cargo test -p loro --test text
• cargo test -p loro-internal --lib
• rustfmt --check crates/loro-internal/src/oplog/change_store.rs crates/loro-internal/src/oplog/change_store/block_encode.rs
• git diff --check

Notes

• pnpm -C crates/loro-wasm build-release was attempted after installing Deno. Rust build, wasm-bindgen, rollup, TypeScript, Vitest, and Deno tests passed, but the final bun test step could not run because bun is not installed in this environment.

[github-actions]

WASM Size Report

• Original size: 3037.14 KB
• Gzipped size: 1001.43 KB
• Brotli size: 703.08 KB