fix: price interpolation (#1154)

Use forward fill to interpolate time series data that represents prices:
- elecprice_marketprice_wh
- feed_in_tariff_wh

Signed-off-by: Bobby Noelte <b0661n0e17e@gmail.com>

tests/single_test_optimization.py

@@ -153,6 +153,7 @@ async def prepare_optimization_real_parameters() -> GeneticOptimizationParameter
         key="elecprice_marketprice_wh",
         start_datetime=prediction_eos.ems_start_datetime,
         end_datetime=prediction_eos.end_datetime,
+        fill_method="ffill",
     )
     print(f"strompreis_euro_pro_wh: {strompreis_euro_pro_wh}")