input: Write a function that takes a list of integers and returns a list of tuples where each tuple contains the index of the number and the square of that number. The output should be in the format [(index, squared_value)].
  assert square_index([1, 2, 3, 4, 5])==[(0, 1), (1, 4), (2, 9), (3, 16), (4, 25)]
  assert square_index([-1, -2, -3])==[(0, 1), (1, 4), (2, 9)]
  assert square_index([])==[]
output: def square_index(lst):
      return [(i, x**2) for i, x in enumerate(lst)]