It's not needed now for testing the flickering.

It is enough to create a portal with that dummy ref-ed container.

This simplifies code and makes parentRef obsolete.

Turns out the issue was also at parent getting rerenders.
So the trick is that I added an empty div with ref for parent node and,
next to it, the Graph component pointing to that ref.
Graph component calls react's usePortal with that parent ref and a small
'createElement' div to hold sigma canvases.

Well, it still does a bit because parent keeps rerendering but we can
manage that.

Also, attempt to make automatic FA pause almost working.

I.e. no data is reloaded so there is less graph flickering.

Now state change doesn't refresh the graph.

This also simplifies numerous useEffect calls.
Still needs work -- graph doesn't render currently, but the code
compiles at least.