feat: add EnergyCharts feed-in tariff provider (#1165)

The `FeedInTariffEnergyCharts` provider uses the raw Energy-Charts day-ahead market price as the
feed-in tariff. It stores prices in `feed_in_tariff_wh` without adding electricity import charges
or VAT. The data is loaded from the Energy-Charts `/price` endpoint for the configured bidding
zone. The native Energy-Charts resolution, including quarter-hour data, is retained.

Energy-Charts usually supplies prices only for the published day-ahead period. If that data does
not cover the complete configured prediction horizon, the provider extends it as follows:

- With more than 800 hours of history, an ETS (Holt-Winters exponential smoothing) forecast with
  weekly seasonality is used.
- With more than 168 hours of history, an ETS forecast with daily seasonality is used.
- With less history, the median of the available values is used as a constant fallback.

The seasonal periods are adjusted to the source resolution. For example, quarter-hour data uses
four values per hour. Values already supplied by Energy-Charts are kept unchanged; only missing
future slots after the last published price are forecast. Consequently, a 15-minute optimization
uses four forecast values per hour without converting them to hourly averages.

Signed-off-by: Andreas Schmitz <akkudoktor.net>
Signed-off-by: Bobby Noelte <b0661n0e17e@gmail.com>

src/akkudoktoreos/prediction/prediction.py

@@ -36,6 +36,7 @@ from akkudoktoreos.prediction.elecpriceenergycharts import ElecPriceEnergyCharts
 from akkudoktoreos.prediction.elecpricefixed import ElecPriceFixed
 from akkudoktoreos.prediction.elecpriceimport import ElecPriceImport
 from akkudoktoreos.prediction.elecpricetibber import ElecPriceTibber
+from akkudoktoreos.prediction.feedintariffenergycharts import FeedInTariffEnergyCharts
 from akkudoktoreos.prediction.feedintarifffixed import FeedInTariffFixed
 from akkudoktoreos.prediction.feedintariffimport import FeedInTariffImport
 from akkudoktoreos.prediction.loadakkudoktor import (
@@ -81,6 +82,7 @@ elecprice_energy_charts = ElecPriceEnergyCharts()
 elecprice_fixed = ElecPriceFixed()
 elecprice_import = ElecPriceImport()
 elecprice_tibber = ElecPriceTibber()
+feedintariff_energy_charts = FeedInTariffEnergyCharts()
 feedintariff_fixed = FeedInTariffFixed()
 feedintariff_import = FeedInTariffImport()
 loadforecast_akkudoktor = LoadAkkudoktor()
@@ -106,6 +108,7 @@ def prediction_providers() -> list[
         ElecPriceFixed,
         ElecPriceImport,
         ElecPriceTibber,
+        FeedInTariffEnergyCharts,
         FeedInTariffFixed,
         FeedInTariffImport,
         LoadAkkudoktor,
@@ -134,6 +137,7 @@ def prediction_providers() -> list[
         elecprice_fixed, \
         elecprice_import, \
         elecprice_tibber, \
+        feedintariff_energy_charts, \
         feedintariff_fixed, \
         feedintariff_import, \
         loadforecast_akkudoktor, \
@@ -158,6 +162,7 @@ def prediction_providers() -> list[
         elecprice_fixed,
         elecprice_import,
         elecprice_tibber,
+        feedintariff_energy_charts,
         feedintariff_fixed,
         feedintariff_import,
         loadforecast_akkudoktor,
@@ -187,6 +192,7 @@ class Prediction(PredictionContainer):
             ElecPriceFixed,
             ElecPriceImport,
             ElecPriceTibber,
+            FeedInTariffEnergyCharts,
             FeedInTariffFixed,
             FeedInTariffImport,
             LoadAkkudoktor,