Return ensembled predictions even when alpha is None

[gmartinonQM]

Hi all, and thanks you so much for developping MAPIE !

I recently hit a limitation of MapieRegressor and MapieTimeSeriesRegressor : I would like to get the ensembled predictions (using the ensemble=True argument in .predict()), but without computing any confidence interval. So I used alpha=None, but in this case, the ensemble argument is ignored, since the code returns immediately the single_estimator_ predictions.

However, it might be that we still want to extract the ensembled prediction (which is easily available in MAPIE class internals) even when alpha=None, given that the computation of this prediction is rather involved.

So it appears that there is an unnecessary coupling between alpha=None and the ability to retrieve ensembled predictions.

Would it be possible to decouple these two quite different things ?