test: saving and loading StateDataClass objects

[hollandjg]

Description

Add robust testing of saving and loading StateDataClass objects using the following modules:

• pickle (default)
• dill
• pyyaml

either saving to and loading from a:

• byte-string, or
• file on disk

Not included here:

• Testing of StateDict, because blocked by

  • refactor: remove aliases from state.py  #49
  • fix: recursion bug on unpickling in the StateDict #51

• resolves test: add robust testing of the State #53

Type of change

• test: Adding missing tests or correcting existing tests

Features

• add hypothesis tests of:
  • StateDataClass
  • Variable (required by StateDataClass)
  • VariableCollection (required by StateDataClass)
• Add new ValueType for boolean and integer (for completeness)

ToDo:

• Fix errors due to too slow

[hollandjg]

Issue: need to speed up example generation for the state object so we can reintroduce the too_slow health check

[younesStrittmatter]

Loving this. To be honest, I don't have the expertise to review this super throughly but I ran it and read through the code. I think I have a grasp on it and understand it, but would not be able to spot errors easily. We should work on adapt this to other parts of autora though (at least to core contributions).