metering 0.16.0

German energy metering domain library — Europe/Berlin calendar arithmetic (DST-correct interval counts), interval types, Gas conversion (m3→kWh_Hs), billing period aggregation (Spitzenleistung, HT/NT), SLP/RLM/iMSys classification, Mehr-/Mindermengensaldo, and Hampel-filter quality scoring. Zero I/O, no async, no clock, exact decimal quantities.