Performance: benchmark and find slow loading widgets

Some base widgets cause the app's slow loading, which blocks the app from loading and gives a bad user experience.
After the widgets is used in the app, it is hard to distinguish which widget causes the long time loading.
Having a dedicated CI test for every widget in the repo will be helpful in locating the widget.
The plan is to have a benchmark notebook for widgets that will import widget class, create instances and show the widget.

At the moment, aiidalab apps including ABW can use https://github.com/aiidalab/aiidalab-test-app-action to do the test, it supports open notebook making screenshots, and also run a specific test on the browser.
We can extend it to run a benchmark unit test for each widget.