test(charging-station): add Transaction Management tests

test(charging-station): add Transaction Management tests

Implement 17 tests covering transaction query methods, energy meters,
transaction state management, and concurrent transaction scenarios.

- Add transaction query tests: hasTransaction, getConnectorIdByTransactionId
- Add energy meter tests: getEnergyActiveImportRegisterByTransactionId
- Add state management tests: isRegistered, stationInfo properties
- Add concurrent transaction tests: hasEvses checks
- Enhance ChargingStationTestUtils with 6 transaction helper methods

All 217 tests pass.