feat(diff): implemented native UTF-16 diff processing and removed jsdiff

- Implemented native UTF-16 text processing in Rust diff module with support for unpaired surrogates.
- Removed `similar` crate from Rust workspace and `diff` npm package from coding-agent, hashline, and natives.
- Removed jsdiff fallback wrappers and `isWellFormed()` guards from TypeScript diff implementations.
- Added comprehensive test suite for native diff functions covering random inputs and edge cases including surrogates and emoji.
- Renamed model `codex-auto-review` to `gpt-5.3-codex-spark` with updated pricing and context window.

packages/typescript-edit-benchmark/package.json

@@ -38,6 +38,7 @@
     "@oh-my-pi/pi-coding-agent": "catalog:",
     "@oh-my-pi/pi-utils": "catalog:",
     "diff": "catalog:",
+    "@oh-my-pi/pi-natives": "catalog:",
     "prettier": "catalog:",
     "regexp-tree": "catalog:",
     "@oh-my-pi/pi-ai": "catalog:",