CQR typing corrections

[LacombeLouis]

Describe the bug
For MapieQuantileRegressor the fit and predict have a # type: ignore for the moment due to typing issues during the implementation. The issue seemed to come from the fact that MapieQuantileRegressor is a child class of MapieRegressor, however, this typing error did not occur in other methods such as time_series_regression.py, so it would interesting to investigate why this occurs of MapieQuantileRegressor.

To Reproduce
Steps to reproduce the behavior:

1. Go to quantile_regression.py
2. Scroll to fitor predict and delete the # type: ignore.
3. Run make type-check in the terminal and you will get the errors mentionned.