def _fit(self, series: TimeSeries, future_covariates: Optional[TimeSeries] = None):
        """Fits/trains the model on the provided series.
        DualCovariatesModels must implement the fit logic in this method.
        """
Fits/trains the model on the provided series.
        DualCovariatesModels must implement the fit logic in this method.
        
darts/models/forecasting/forecasting_model.py