code: def _find_solo_consonant(self, letters: List[str]) -> List[int]:
          
          solos = []
          for idx, letter in enumerate(letters):
              if len(letter) == 1 and self._contains_consonants(letter):
                  solos.append(idx)
          return solos
docs: Find the positions of any solo consonants that are not yet paired with a vowel.