Include TexGen instead of going through PuMa

Directly include TexGen instead of going through PuMa.
We have to wait for the conda package PR (https://github.com/conda-forge/staged-recipes/pull/31077) of TexGen by @claudiushaag to go through, and then include TexGen directly in a subsequent patch.

Also depends on https://github.com/louisepb/TexGen/issues/70