input: Write a python function to return a list of tuples with the index and the square of each number in the input list.
  assert square_index([1, 2, 3, 4, 5]) == [(0, 1), (1, 4), (2, 9), (3, 16), (4, 25)]
  assert square_index([0, -1, -2, -3, -4]) == [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16)]
  assert square_index([10, 20, 30]) == [(0, 100), (1, 400), (2, 900)]
output: def square_index(lst):
      return [(i, x ** 2) for i, x in enumerate(lst)]