Return a tuple from `get_evaluation` instead

[johndoknjas]

The dict that's returned from get_evaluation is a bit confusing, especially because one of the two keys is called "value". If we instead return a Tuple[str, int], that feels like it could be simpler.
However, there are backwards compatibility issues, as existing users might get a tuple and assume they still get a dict. If they do something like iterating over the keys of the dict, this would now iterate over the values of the tuple.