input: Write a python function to find and return the minimum and maximum values in a list.
  assert find_min_max([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]) == (1, 9)
  assert find_min_max([-7, -3, -2, -1, 0, 1, 2, 3, 7]) == (-7, 7)
  assert find_min_max([10, 20, 30, 40, 50]) == (10, 50)
output: def find_min_max(lst):
      if not lst:
          return None, None
      min_val = min(lst)
      max_val = max(lst)
      return min_val, max_val