Demos should be refactored to be consistent with modern react standards and styles

[Cpt-Falcon]

Demos are still using very old class style components

[kilotone]

Might benefit from using state/effect and custom hooks as well. I extended custom components using react fc and some material and joyui components, was fairly straightforward, but adding custom hooks would really shine for the equivalent of useModel, useSerialize useFlowState, and useDiagramTransition.

[kilotone]

I was able to mostly migrate to functional components and hooks, the only problems seemed to be the class components use of force update calls, and some dangerously set innerhtml.
I can submit a pr if there's interest.