Increase performance by only predicting on most recent candle instead of full strat provided dataframe. Collect predictions and store them so that we can feed true predictions back to strategy (so that frequi isnt updating historic predictions based on newly trained models).

freqtrade/freqai/data_kitchen.py

@@ -623,7 +623,7 @@ class FreqaiDataKitchen:
         Append backtest prediction from current backtest period to all previous periods
         """
 
-        ones = np.ones(len_dataframe)
+        ones = np.ones(len(predictions))
         target_mean, target_std = ones * self.data["target_mean"], ones * self.data["target_std"]
 
         self.full_predictions = np.append(self.full_predictions, predictions)