migrate python-focused 'binder' image out of rocker-versioned2

[cboettig]

@eitsupi are we still building the binder image as part of the extra group here? In light of #903, I was thinking we could move that back to the rocker-org/binder repository. I'm interested in applying the elegant apt-based approach there to sidestep the apt issues and also align the binder image more directly with the (conda-based) Jupyter docker stacks.

[eitsupi]

CI is broken and has not been updated recently.

I certainly don't think many users are interested in fixing the version, so it makes more sense to move on, and on the side of using Python from R, it looks like reticulate is rapidly steering towards the use of uv these days, so I'm not sure if apt-installed Python is the way to go.
People may not want to use it.

[cboettig]

thanks, sounds like a plan. I'll refresh the binder image.

@eddelbuettel apologies for my short-hand, I'll do better to give credit where it is due! I only meant to acknowledge that among the rocker maintainers, you have often spoken on the merits of that approach to binary management, as you have on apt-based Debian ecosystem to which you are a long-standing contributor! r2u may be a thin but to my mind very nice addition to the bspm mechanism, which itself obviously builds on the apt/debian systems that represent the contributions of more than any one individual. but point taken, I'll edit the above so this can self-destruct too :-)