Automated widget testing

[kylebarron]

There's now pytest-ipywidgets.

See jupyter-widgets/ipywidgets#2934 (comment). Note that this might still be quite difficult to implement because we need to emulate a GPU as well if we want to render data. I believe deck used some setup with xvfb to emulate the GPU in CI

[kylebarron]

Fuller docs: https://solara.dev/documentation/advanced/howto/testing#testing-with-a-browser