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