Write a function that optimizes energy consumption data for reporting at Duke Energy.
Implement optimize_energy_data(readings, interval_minutes). Each reading is a dictionary with an integer timestamp in minutes and numeric kwh consumption. Return one dictionary per reporting interval, summing all readings whose timestamps fall in that interval, ordered by interval start time. Return an empty list when no readings are provided.
The interval containing timestamp t starts at (t // interval_minutes) * interval_minutes.
def optimize_energy_data(readings, interval_minutes):