MAINT create a specific scorer base class for curve metrics

[glemaitre]

roc_curve and precision_recall_curve are not usual score metric since they return array of two metrics parametrized by an array of threshold. If used with make_scorer, these methods would be passed to _Scorer class. However, this is an abuse of this class since it is expected to only return a scalar.

We should therefore create another base class specifically for these curve score metrics. A specific use case where these metrics will be used is internally to TunedThresholdClassifierCV: #26120

The design of such _CurveScorer should allow to simplify the internal design and we should have stronger tests as well. make_scorer should call this class as well.