input: Write a python function to save level placement details into a temporary file using pickle.
  assert save_levels() == 'Saved level placement to tempfile' # Assuming this test case passes
  assert save_levels() == 'Nothing to save' # Assuming no levels are selected
output: import pickle
  import tempfile
  
  def save_levels(levels=None):
      if levels is None or not levels:
          return 'Nothing to save'
      
      with tempfile.NamedTemporaryFile(delete=False) as temp_file:
          pickle.dump(levels, temp_file)
          
      return 'Saved level placement to tempfile'