US energy benchmark prices from the EIA (Energy Information Administration) open data API. Omit series for a one-call snapshot of the latest value of every benchmark; pass series for its recent time series (newest first). Benchmarks: wti_crude / brent_crude ($/barrel), henry_hub_gas ($/MMBtu), gasoline_regular / diesel ($/gallon), electricity_retail (cents/kWh). Each observation has date, value, units, and frequency. Public-domain US government data.