rebber: implement the new tables system

[StaloneLab]

The tabu LaTeX package does not work with TeXLive versions greater than or equal to 2020. I suspect some distributions might include fixes to mitigate the issue for some time, but we should not depend on this.
Some work was done on the template repository to assess the possible alternatives, of which tabularray seems to be the best candidate (see zestedesavoir/latex-template#137, in French).

I started experimenting with the package and might be able to implement something in the upcoming weeks, which I plan to release as version 12.0.0 once done, maybe with some other updates. The MDAST side should change as little as possible, to accommodate changes started in the next branch.