test: restore and harmonize OCPP 2.0 transaction meter value assertions

test: restore and harmonize OCPP 2.0 transaction meter value assertions

- Add symmetric buildTransactionEndedMeterValues tests via requestStopTransaction
  (context=Transaction.End, measurand=Energy, no config key, no EVSE template)
- Strengthen buildTransactionStartedMeterValues assertions with strict
  context and measurand checks using OCPP enum constants
- Refactor Started tests: shared station setup in beforeEach, remove duplication
- Configure TxEndedMeasurands in deauthorization test for real coverage
- Remove comments that restate test names