Write in Python or pseudocode a function called heap_children. The function takes as input a list a containing a binary heap and an index i. It returns a tuple with the values of the left and right children corresponding to the element contained in a[i]. The tuple should contain None in place of the value of a non existing child. The function's signature is as follows: def heap_children( a: list[int], i: int ) -> tuple[Optional[int], Optional[int]]: Usage examples: >>> heap: list[int] = [1, 3, 6, 5, 9, 8] >>> heap_children(heap, 1) (5, 9) >>> heap_children(heap, 2) (8, None) And can you explain to me the whats the overall explanation