add example which registers and uses go custom elements

this example has an assert that checks wether or nor the finalizers ran correctly. If they don't then a mem leak will happen

examples/plugins/registered_elements/internal/common/util.go

@@ -0,0 +1,9 @@
+package common
+
+func Must[T any](v T, err error) T {
+	if err != nil {
+		panic("got error:" + err.Error())
+	}
+
+	return v
+}