experimental: Gröbner Walk

[ooinaruhugh]

This PR supercedes #3131 and provides some variants of the Gröbner Walk.
Currently, this includes

• Standard walk from Collart, Kalkbrener and Mall (1997)
• Generic walk from Fukuda (2007)
• Perturbed walk from Amrhein, Gloor and Küchlin (1997)

Further things we want to do:

• feat: Groebner Walk #3131 included some more variants, we're still in the process of revising those.
• Also, the code probably needs some tidying up.
• We're currently investigating whether we can improve the performance of this implementation.
• Tests

[fingolfin]

We just discussed this during triage. @ederc is fine with the "big picture" (we can improve details later). @afkafkafk13 is as well happy with it, but would like to have another look before approving.

Since this is big and has been around, it indeed seems sensible to me to merged this rather sooner and fine tune it later, but I'll leave it to the experts to make the final call.

[ooinaruhugh]

Yeah, I agree with that. As far as I can tell, I addressed most of the previous remarks and the implemented algorithms do work correctly. I would also prefer to do any additions in a future PR.