refactor(ocpp): extract version-specific builders and transaction operations
Extract meter value builders into OCPP16/20MeterValueBuilders.ts leaf
modules. Extract boot notification builders into OCPP16/20RequestBuilders.ts
leaf modules. Move buildBootNotificationRequest dispatcher from Operations
to Utils. Extract OCPP 2.0 startTransactionOnConnector and
stopTransactionOnConnector into OCPP20ServiceUtils, removing inline
OCPP 2.0 enums and logic from the shared Operations module.