Implement OCPI CDR and tariff modules for EV roaming billing

Steps

1. Establish an OCPI 2.2.1 connection to the counterparty (eMSP or CPO) or roaming hub: complete the credentials handshake by exchanging tokens via POST /ocpi/2.2.1/credentials and retrieve the versions and module URLs from the returned version detail endpoint.
2. Implement the Tariffs module as a CPO: push tariff objects (containing TariffElement arrays with PriceComponent entries for FLAT, ENERGY, TIME, and PARKING_TIME types, plus TariffRestriction time/day filters) to the eMSP via PUT /ocpi/{version}/tariffs/{country_code}/{party_id}/{tariff_id}.
3. During a charging session, build the CDR (Charge Detail Record) on session close: populate required fields including id, start_date_time, end_date_time, cdr_token, auth_method, cdr_location, currency, tariffs (snapshot at session start), charging_periods (per-interval energy and time), total_cost, and total_energy.
4. For Credit CDRs (introduced in OCPI 2.2.1 to handle billing corrections), set the credit flag to true and reference the original CDR id in the credit_reference_id field; push via POST /ocpi/{version}/cdrs.
5. Include Calibration Law / Eichrecht fields in CDRs where legally required (Germany and other EU markets): populate the signed_data field with the meter's signed OCMF or EDIFACT payload for legal admissibility of the energy measurement.
6. Reconcile CDR totals: verify that total_cost equals the sum of cost across all ChargingPeriods after applying tariff rules; mismatches cause eMSP rejection — implement a pre-submission validation step.