Add some typing to tests

[mathbunnyru]

Main change is to add some typing, but there are some other changes as well.
Sorry they are all packed in one PR, but there are no significant changes here.

[mathbunnyru]

Forgot to mention this - with typing, implementing new changes becomes easier (IDEs like VS Code do much much better with typing).
And, I didn't add typing in all possible places, but I think this is better than nothing.

[consideRatio]

LGTM!! I haven't used these type annotations actively and have little experience overall, but it sounds very reasonable to go for!

[mathbunnyru]

amd64 works fine, so merging this.