refactor: encapsulate connector/EVSE iteration behind generator API

refactor: encapsulate connector/EVSE iteration behind generator API

Introduce iterateConnectors() and iterateEvses() generators on
ChargingStation, replacing ~30 duplicated if(hasEvses)/else iteration
patterns across the codebase. Make connectors and evses Maps private
to enforce usage of the new API.

- Add ConnectorEntry and EvseEntry as unified types for both iteration
  and serialization, removing duplicate ConnectorDataEntry/EvseDataEntry
- Add hasEvse() accessor method for EVSE existence checks
- Fix remoteStartId not propagated in TransactionEvent (F01.FR.25)
- Fix messagesInQueue in GetTransactionStatus to check actual queue
- Fix OCPP 1.6 changeAvailability losing SCHEDULED response
- Consolidate ad-hoc test mock factories to use createMockChargingStation
- Update UI wire format and components for unified types

BREAKING CHANGE: connectors and evses Maps are now private on
ChargingStation. Use iterateConnectors(), iterateEvses(), hasEvse(),
getEvseStatus(), getConnectorStatus() instead of direct Map access.