cache static method
Implementation
static Future<String?> cache(String filePath) async {
final file = File(filePath);
if (!file.existsSync()) return null;
final baseDir = await getCachePath();
if (baseDir == null) return null;
final outputPath = join(baseDir, '${genDateSign()}${extension(filePath)}');
return (await file.copy(outputPath)).path;
}