input: Write a python function to count the number of positive elements in the last 5 elements of an array.
  assert count_positive_last5([-3, 9, 2, 10, -5, 4, 3]) == 3
  assert count_positive_last5([1, -1, -1, 1, 1, 1, -1]) == 3
  assert count_positive_last5([0, 0, 0, 0, 0, 0, 0]) == 0
output: def count_positive_last5(arr):
      return sum(1 for x in arr[-5:] if x > 0)