fixtures: some type annotations, remove cyclic dependency

[bluetech]

Please see the two commits.

[RonnyPfannschmidt]

Looks lovely overall, thanks

[RonnyPfannschmidt]

Should be plain marks as well

[bluetech]

Thanks for the review.

It seems that plain mark is not accepted here -- this function calls self.node.add_marker(marker) which starts with

        from _pytest.mark import MARK_GEN

        if isinstance(marker, MarkDecorator):
            marker_ = marker
        elif isinstance(marker, str):
            marker_ = getattr(MARK_GEN, marker)
        else:
            raise ValueError("is not a string or pytest.mark.* Marker"

[aklajnert]

I always considered using dicts better than a chain of elifs. What's the rationale behind it?

[bluetech]

Good question, the reasons I changed it are:

• Due to the cyclic dependency it used to be initialized in a funky way in a hook. (There is still a cycle with _pytest.python so the second commit doesn't solve this.)

• With the if/elif chain the logic can be localized in one place which IMO is a bit easier to follow.

• I can use assert_never which means that if a new scope is ever added it will automatically trigger a mypy warning if a case for the new scope isn't added.

• Another reason I see now is that coverage doesn't work a "dict conditional" but works well with a chain of ifs.

[aklajnert]

I think that the assert_never can still be used with dicts.
Anyway, all the reasons make sense, thanks for explaining.

[nicoddemus]

Great work!