[util] improve performance of type check

[clonker]

Small change to improve performance of check whether is something a list of int by a factor of roughly 20:
Old implementation on list of 1000000 random ints:

861 ms ± 9.3 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

New implementation on list of 1000000 random ints:

48.3 ms ± 932 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

Fixes #1439

[marscher]

That's brilliant, did you come up with the groupby type idea? 👍

[marscher]

the failed MSM tests are due to a change of version in openblas, I have reported it on Conda-forge (since it is actually on an increase in build number, not source code version) conda-forge/blas-feedstock#40

[clonker]

What can I say, cosmic radiation! 🤷‍♂️

[marscher]

The speed penalty of the old impl has to arise from the boolean and operations per element, not the type check. Since groupby reduces the boolean operations to the amount of types in the list, it is blazingly fast ⚡