rounding.py is excluded from github actions

[TolisChal]

The test file sampling.py is not included in the github actions.
However, when I added it fails.

[vfisikop]

sampling.py is included in github actions and runs correctly but rounding.py is not included and it fails if added.

[vfisikop]

I reopen it since we have to find a way to run gurobi based tests on CI.

[hariszaf]

This is possible but we will have to update or extend the license from time to time.
What we need is a Web License Service

[vissarion]

Also there is non gurobi rounding version. And this exposes a deeper issue: the slow_* and fast_* function design where there is a lot of duplicate code and they are difficult to maintain or extend. This could be (partially) fixed by designing a more generic interface to lp solvers (see #84).

[hariszaf]

Then it's maybe better instead of going through the WLS task, to work on the #84 so we move to optlang

"Optlang provides a common interface to a series of optimization tools, so different solver backends can be changed in a transparent way."

so we do not care of maintaining more than one implementations for the same task