test: add type hints for test_storage

[tonyandrewmeyer]

• Ignore the Nones passed when creating the framework - passing real values would be a lot of extra noise without actually gaining any value in the test
• Add dummy methods to make the Serializable protocol match
• Ignore types when replacing a (when type checking) property
• Inherit from StoredStateData rather than Object to match the type of the Framework.save_snapshot method - the additional methods seem harmless in this case, and the meaning of the test seems unchanged
• Sprinkle enough type hints so that pyright can tell what's happening

Partially addresses #1007

[benhoyt]

LGTM, thanks!

[benhoyt]

Minor typing additions to test files, merged without further review.