save method
Saves cache to disk.
Implementation
Future<void> save() async {
final file = File(_cachePath);
final dir = file.parent;
if (!dir.existsSync()) {
dir.createSync(recursive: true);
}
final entries = _cache.entries.map((e) => e.value.toJson(e.key)).toList();
final json = jsonEncode({'entries': entries, 'version': 1});
await file.writeAsString(json);
}