stat method
File facts for staleness guards; null when the file is gone.
Implementation
Future<({int size, int mtimeMs})?> stat() async {
final result = await fs.fileInfo(path);
if (result.isErr) return null;
final info = result.valueOrNull!;
if (info.kind != FileKind.file) return null;
_noteParseCacheStamp(info.size, info.mtimeMs);
return (size: info.size, mtimeMs: info.mtimeMs);
}