text: Title: Ensure ClassificationScoreVisualizers subclasses return score and add tests
  Body: Extended from #361 to be more specific. In #407 we reworked the `ClassificationScoreVisualizer` to save the score in a `score_` property, then return it from the method after drawing. We still need to update the subclasses to either call `super()` or ensure that they implement the behavior described above. 
  
  - [ ] `ClassPredictionError` should return an `self.estimator.score()` but already stores `score_`; requires test to ensure it returns a score between 0 and 1. 
  - [ ] `ClassificationReport` should return `self.estimator.score()` but already stores `score_`; requires test to ensure it returns a score between 0 and 1. 
  - [ ] `ConfusionMatrix` should return `self.estimator.score()` and store `score_` (it keeps its references in a `confusion_matrix_` property. Requires a test to ensure it returns a score between 0 and 1. 
  - [ ] `ROCAUC` already returns a score property. Check to make sure it has a test for the score. 