test(charging-station): complete Wave 2 - boot notification and configuration tests

test(charging-station): complete Wave 2 - boot notification and configuration tests

Task 6 - Boot Notification State (6 tests):
- State query methods: inAcceptedState, inPendingState, inRejectedState, inUnknownState
- State transitions: PENDING → ACCEPTED/REJECTED
- Boot response structure validation

Task 7 - Configuration Persistence (14 tests):
- OCPP config getters: getHeartbeatInterval, getConnectionTimeout, etc.
- Configuration save and persistence verification
- Mock filesystem validation (no real I/O)

Wave 2 Complete: 54 total tests
- Lifecycle: 11 tests
- Connector/EVSE: 22 tests
- Boot Notification: 6 tests
- Configuration: 14 tests

Fixed ESLint errors in test utilities