input: Write a function to find the position of the maximum value in a 2D matrix.
  assert max_pos([[2, 8, 7], [3, 11, 5], [1, 9, 4]]) == (1, 1)
  assert max_pos([[1, 2, 3], [4, 5, 6], [7, 8, 9]]) == (2, 2)
  assert max_pos([[0, -1, -2], [-3, -4, -5], [-6, -7, -8]]) == (0, 0)
output: def max_pos(matrix):
      max_value = float('-inf')
      max_position = (-1, -1)
      for i, row in enumerate(matrix):
          for j, value in enumerate(row):
              if value > max_value:
                  max_value = value
                  max_position = (i, j)
      return max_position