Live plotting

[fcasson]

When debugging a case that would not progress due to falling timestep, I found live plotting useful.

My agent added something that helped me figure out what was going wrong, and while it is probably not general enough for a PR, it might be enough to stimulate a design / requirements discussion: main...fcasson:torax:feature/live-plot

[jcitrin]

Once upon a time we had live plotting, via "spectators".

Removed here #608 since the way it was done wasn't aligned with the overarching design direction, but we never redesigned it and put it back. I agree that it would be good to do so, reusing the plotruns_lib and the plot_configs.

We can discuss with @Nush395 , @sbodenstein , @tamaranorman and converge on a design doc. I'll make a first stab and share it