input: Write a python function to generate permutation of two strings by interleaving their characters.
  assert generate_permutation("abc", "xyz") == "axbycz"
  assert generate_permutation("123", "abc") == "1a2b3c"
  assert generate_permutation("hello", "world") == "hweolrllod"
output: def generate_permutation(s1, s2):
      result = []
      len_s1, len_s2 = len(s1), len(s2)
      for i in range(max(len_s1, len_s2)):
          if i < len_s1:
              result.append(s1[i])
          if i < len_s2:
              result.append(s2[i])
      return ''.join(result)