docs: add documentation for v1.2.1 features

Added minimal documentation for new features in Bun v1.2.1:
- S3 storageClass option in presign
- X25519 support in crypto.generateKeyPair
- Indented inline snapshots in bun test
- --zero-fill-buffers CLI flag
- HTML minify option in bunfig.toml
- fs.fstatSync bigint option support
- dgram reuseAddr/reusePort socket options
- Buffer.toLocaleString alias

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/api/binary-data.md

@@ -420,6 +420,8 @@ console.log(buf.toString());
 // => Hello world
 ```
 
+`Buffer.prototype.toLocaleString` is an alias for `Buffer.prototype.toString`.
+
 For complete documentation, refer to the [Node.js documentation](https://nodejs.org/api/buffer.html).
 
 ## `Blob`