getAyah method
Get a specific ayah by its number
Implementation
Ayah? getAyah(int ayahNumber) {
  if (ayahNumber < 1 || ayahNumber > numberOfAyahs) {
    return null;
  }
  return ayat.firstWhere(
    (ayah) => ayah.id == ayahNumber,
    orElse: () =>
        throw ArgumentError('Ayah $ayahNumber not found in surah $id'),
  );
}