hasFontForPage method
Checks if a font file for pageNumber (1-based) exists in cache.
Implementation
Future<bool> hasFontForPage(int pageNumber) async {
final dir = await getCacheDir();
final file = File('${dir.path}/QCF4_tajweed_${pageNumber.toString().padLeft(3, '0')}.ttf.gz');
return file.existsSync();
}