startSession method
Implementation
SessionState startSession({String? model, String? provider}) {
final id = 'session_${DateTime.now().millisecondsSinceEpoch}';
_session = SessionState(
id: id,
activeModel: model ?? _activeModel,
activeProvider: provider ?? _activeProvider,
);
_eventController.add(SessionStarted(id));
return _session!;
}