Test 1
Write the function list_sum that takes aribtrary number of lists and returns a list whose values are the element-wise sum of the input lists.
list_sum([1, 2, 3], [4, 5, 6]) -> [5, 7, 9]
list_sum([1, 2, 3], [4, 5, 6], [100, 200, 300]) -> [105, 207, 309]