Add tests for dataclasses that use Slots and Keyword-Only options.

[brocla]

A test is added to verify that the new dataclass features, slots and kw_only, can be parsed by the Representer.

The three examples used are: sgf_parsing, go_counting, and tree_building. They were chosen because their solutions already use dataclasses, making it easier to demonstrate the new features.

[brocla]

The test is failing on this PR because of code like this,

@dataclass(slots=True)   #***
class Record:
    record_id: int
    parent_id: int = field(kw_only=True)

Perhaps I don't have access to the latest update that fixed this issue. I'm a bit stuck.

[BethanyG]

I'll take a look.