add print statement to NCC if instantiated with date before its introduction

[eglucas]

add print statement (similar to that in NRAB) to levies.py - NCC class - from_dataframe() L1078

# Alert message if price cap period pre-dates ncc
if price_cap_date < pd.to_datetime("2025-04-01"):
print(f"Selected date {price_cap} pre-dates introduction of NCC levy. Levy object will not contain any levy rates.")