input: Write a python function to increment each number in a list by 1.
  assert custom_function([2, 3, 1, 4]) == [3, 4, 2, 5]
  assert custom_function([0, -1, -2, -3]) == [1, 0, -1, -2]
  assert custom_function([100, 200, 300]) == [101, 201, 301]
output: def custom_function(lst):
      return [x + 1 for x in lst]