fix(ocpp): drive FirmwareStatusNotification trigger from last-sent notification ...

fix(ocpp): drive FirmwareStatusNotification trigger from last-sent notification (L01.FR.26) (#1981)

TriggerMessage(FirmwareStatusNotification) was gated on
`activeFirmwareUpdateRequestId != null && hasFirmwareUpdateInProgress()`,
falling back to Idle otherwise. Since `hasFirmwareUpdateInProgress` returns
false for every terminal status (`DownloadFailed`, `InvalidSignature`,
`InstallationFailed`, `InstallVerificationFailed`, `Installed`), the
station returned Idle after every non-Installed terminal, violating OCPP
2.0.1 L01.FR.26 (SHALL, mirrored by L02.FR.17).

Persist the last-sent `(requestId, status)` on `OCPP20StationState` and
drive the trigger from it. `stationInfo.firmwareStatus` is retained
because `hasFirmwareUpdateInProgress` and its 3 consumers (reset
rejection, isChargingStationIdle, isEvseIdle) depend on its
"in-progress predicate" semantics — deliberate dual-source, not
conflation.

Closes #1979