Allow using Test.runtests in other packages

[blegat]

Would be useful for blegat/LowRankOpt.jl#6 for instance

[odow]

I'm not necessarily for or against this. One massive downside is that we'd be committing to the API Innside this function. I don't know that it's worth it to save a single package (LowRankOpt) copy-pasting a single function. Especially if the long-term goal is to merge some form of LowRankOpt back into MOI.

[blegat]

I was wondering about how much more we're committing to if the API (name of the function, name of the keywords, behavior) is already public anyway. What would be breaking for a use of test_module that wouldn't be also breaking now anyway ?

[odow]

I'll merge this if https://github.com/jump-dev/MathOptInterface.jl/actions/runs/14327216427 looks okay

(Edit: it's going to look bad for the solvers with secrets because this branch isn't rebased on the latest master.)