Add unit test for all options and bifurcations

Revisit the classifier_helper

Opciones
typeexampleinit
kFCVint10y
heldoutfloat0.6y
sampletupleX,yn

init:
kFCV:Q(val_split=10, random_seed=None)
held:Q(val_split=0.7, random_seed=None)
sample:--

the classifier is not fit:
fit end-to-end (classification->predictions->aggregation):
kFCVfit(X, y, val_split=10)
heldfit(X, y, val_split=0.7) 
samplefit(X, y, val_split=(X,y))

the classifier is fit:
fit only aggregation (predictions->aggregation):
samplefit_aggregation(X, y, transform_X=True)

fit only aggregation (aggregation):
samplefit_aggregation(P, y, transform_X=False)