input: Write a python function to validate if a given matrix is a multiplication table of consecutive integers.
  assert is_valid_mul_table([[1, 2, 3], [2, 4, 6], [3, 6, 9]]) == True
  assert is_valid_mul_table([[1, 2], [3, 4]]) == False
  assert is_valid_mul_table([[1, 3], [2, 6]]) == False
output: def is_valid_mul_table(matrix):
      n = len(matrix)
      if n == 0 or any(len(row) != n for row in matrix):
          return False
  
      expected_row = list(range(1, n+1))
      for i in range(n):
          for j in range(n):
              if matrix[i][j] != expected_row[i] * expected_row[j]:
                  return False
                  
      return True