input: Write a python function to group strings by their length using defaultdict.
  assert group_strings_by_length(["Apple", "Orange", "Banana", "Pineapple"]) == {5: ["Apple"], 6: ["Orange", "Banana"], 9: ["Pineapple"]}
  assert group_strings_by_length(["hello", "world", "python", "code"]) == {5: ["hello", "world"], 6: ["python"], 4: ["code"]}
  assert group_strings_by_length(["a", "ab", "abc", "abcd", "abcde"]) == {1: ["a"], 2: ["ab"], 3: ["abc"], 4: ["abcd"], 5: ["abcde"]}
output: from collections import defaultdict
  
  def group_strings_by_length(strings):
      length_dict = defaultdict(list)
      for string in strings:
          length_dict[len(string)].append(string)
      return dict(length_dict)