fix(bec_widget): added cleanup method to bec widget base class

bec_widgets/utils/bec_widget.py

@@ -1,2 +1,7 @@
 class BECWidget:
     """Base class for all BEC widgets."""
+
+    def closeEvent(self, event):
+        if hasattr(self, "cleanup"):
+            self.cleanup()
+        event.accept()