Load the actual-load time series from interim/energy_load.csv.
Reads the Actual Load column and converts the index to a UTC DatetimeIndex with hourly frequency. Missing values are rejected by default so callers cannot accidentally feed imputed values into downstream safety-critical pipelines. Pass on_missing='ffill_bfill' to opt into the legacy forward/backward fill behavior that was the default before the 1.0 major release.