Assert on 'valid' call states in calls-history.
See https://source.puri.sm/Librem5/calls/-/issues/169#note_113531 - at least the 'UNKONWN' state maps 'DIALING' but we don't e.g. accept it for 'ENDED'.
We should be more forgiving and rather return an error. Also the UNKNOWN
state deserves special handling.