feat(rpc): discover widgets automatically

tests/unit_tests/test_rpc_widget_handler.py

@@ -0,0 +1,7 @@
+from bec_widgets.cli.rpc_wigdet_handler import RPCWidgetHandler
+
+
+def test_rpc_widget_handler():
+    handler = RPCWidgetHandler()
+    assert "BECFigure" in handler.widget_classes
+    assert "SpiralProgressBar" in handler.widget_classes