input: Write a python function to find the length of the longest common subsequence between two strings.
  assert longest_common_subsequence("python", "honor") == 3
  assert longest_common_subsequence("abcde", "ace") == 3
  assert longest_common_subsequence("abc", "abc") == 3
output: def longest_common_subsequence(s1, s2):
      m, n = len(s1), len(s2)
      dp = [[0] * (n + 1) for _ in range(m + 1)]
      
      for i in range(1, m + 1):
          for j in range(1, n + 1):
              if s1[i - 1] == s2[j - 1]:
                  dp[i][j] = dp[i - 1][j - 1] + 1
              else:
                  dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
      
      return dp[m][n]