input: Write a python function to check if all characters in a string are vowels.
  assert CheckVowel("aeiou").check_vowel() == True
  assert CheckVowel("AEIOU").check_vowel() == True
  assert CheckVowel("aeio").check_vowel() == False
  assert CheckVowel("abc").check_vowel() == False
  assert CheckVowel("EIOU").check_vowel() == False
output: class CheckVowel:
      def __init__(self, string):
          self.string = string
  
      def check_vowel(self):
          vowels = set("aeiouAEIOU")
          return all(char in vowels for char in self.string)