EEP: Patch / Diff for all EDSL objects

[johnjosephhorton]

We should be able to efficiently store changes in edsl objects, like so:

from edsl import QuestionFreeText 
q1 = QuestionFreeText.example()
q2 = QuestionFreeText.example()
q2.question_text = "Here is some new text"
diff_1 = q2 - q1
assert q2 == diff_1 + q1 
diff_2 = q1 - q2 
assert q1 == diff2 + q2

diffs themselves should be coop-able. In terms of implementation, it probably works by doing comparisons of the .dict() methods of the objects. It likely recursively checks if a sub-object has a diff/dict method. As much as possible, it tries to only log modifications of strings / numbers rather than whole-scale replacement of objects. A diff object might have nested diff objects.

Related - sematically the same

We need to decide what it means for two edsl obejcts to be identical.