fs.writeFile/fs.readFile/fs.stat are callback-based and don't return
Promises in the UXP sandbox. await on them resolves immediately, causing
race conditions where files aren't written before import.
Added _writeFile/_readFile/_stat wrappers that use fs.promises when
available and fall back to manual Promise wrapping otherwise.
Also bumped version to 2.2.3 to match web-ui data.jsx.
