Adaptation of Conditional CP method to classification

[Damien-Bouet]

Description

To adapt the CCP method to classification tasks, we need to create a new main class SplitCPClassifier.
The calibrators are the same, as they just use conformity scores (no matter the task).
We will reuse the classification conformity scores, added since the MapieClassifier refacto.

Fixes #499

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• Empirical checks, in a tutorial/demo in the documentation
• Unit tests

Checklist

• I have read the contributing guidelines
• I have updated the HISTORY.rst and AUTHORS.rst files
• Linting passes successfully : make lint
• Typing passes successfully : make type-check
• Unit tests pass successfully : make tests
• Coverage is 100% : make coverage
• Documentation builds successfully : make doc