[Minor] Split prep_or_copy_df into copy and check_multiple_series_id

[ourownstory]

prep_or_copy_df has been called in too many places. In order to reduce complexity and redundant copies, prep_or_copy_df is split into copy and check_multiple_series_id. Calls to both have further been reduced.

[github-actions[bot]]

Model Benchmark

Benchmark	Metric	main	current	diff
PeytonManning	MAE_val	0.35033	0.35033	0.0%	:white_check_mark:
PeytonManning	RMSE_val	0.50095	0.50095	0.0%	:white_check_mark:
PeytonManning	Loss_val	0.01775	0.01775	0.0%	:white_check_mark:
PeytonManning	MAE	0.34667	0.34667	0.0%	:white_check_mark:
PeytonManning	RMSE	0.49357	0.49357	0.0%	:white_check_mark:
PeytonManning	Loss	0.01466	0.01466	0.0%	:white_check_mark:
PeytonManning	LR	0.00032	0.00032	0.0%	:white_check_mark:
PeytonManning	time	14.8359	14.85	0.1%	:white_check_mark:
AirPassengers	MAE_val	30.1315	30.1315	0.0%	:white_check_mark:
AirPassengers	RMSE_val	31.0835	31.0835	0.0%	:white_check_mark:
AirPassengers	Loss_val	0.01242	0.01242	0.0%	:white_check_mark:
AirPassengers	MAE	6.12226	6.12226	0.0%	:white_check_mark:
AirPassengers	RMSE	7.80921	7.80921	0.0%	:white_check_mark:
AirPassengers	Loss	0.00064	0.00064	0.0%	:white_check_mark:
AirPassengers	LR	0.0004	0.0004	0.0%	:white_check_mark:
AirPassengers	time	8.20583	8.31	1.27%	:white_check_mark:
EnergyPriceDaily	MAE_val	5.40186	5.40186	0.0%	:white_check_mark:
EnergyPriceDaily	RMSE_val	6.70655	6.70655	0.0%	:white_check_mark:
EnergyPriceDaily	Loss_val	0.02519	0.02519	0.0%	:white_check_mark:
EnergyPriceDaily	MAE	5.91309	5.91309	0.0%	:white_check_mark:
EnergyPriceDaily	RMSE	7.94008	7.94008	0.0%	:white_check_mark:
EnergyPriceDaily	Loss	0.02554	0.02554	0.0%	:white_check_mark:
EnergyPriceDaily	LR	0.00029	0.00029	0.0%	:white_check_mark:
EnergyPriceDaily	time	19.576	19.55	-0.13%	:white_check_mark:
YosemiteTemps	MAE_val	0.57336	0.57336	0.0%	:white_check_mark:
YosemiteTemps	RMSE_val	0.84714	0.84714	0.0%	:white_check_mark:
YosemiteTemps	Loss_val	0.00042	0.00042	0.0%	:white_check_mark:
YosemiteTemps	MAE	0.93956	0.93956	0.0%	:white_check_mark:
YosemiteTemps	RMSE	1.65601	1.65601	0.0%	:white_check_mark:
YosemiteTemps	Loss	0.00118	0.00118	0.0%	:white_check_mark:
YosemiteTemps	LR	0.0001	0.0001	0.0%	:white_check_mark:
YosemiteTemps	time	58.9391	58.9	-0.07%	:white_check_mark:

Model training plots

## Model Training ### PeytonManning  ### YosemiteTemps  ### AirPassengers  ### EnergyPriceDaily