input: Write a python function to sort a list of strings by their length.
  assert sort_by_char_length(["apple", "banana", "cherry", "date"]) == ["date", "apple", "banana", "cherry"]
  assert sort_by_char_length(["a", "bbb", "cc"]) == ["a", "cc", "bbb"]
  assert sort_by_char_length(["longest", "longer", "long"]) == ["long", "longer", "longest"]
output: def sort_by_char_length(strings):
      return sorted(strings, key=len)