Non-identical results on different platforms

[danieledler]

Infomap uses the Mersenne Twister pseudo-random generator that is included in the standard library (std::mt19937), however the implementation of that differ on different platforms.

This makes it harder to replicate exact results across platforms, and to construct automated tests.

A recent build failure is due to a doctest example in Python failing in the Github action runner as the order of nodes differ from the that on my local Mac.

See also igraph/igraph#2646 (comment) by @vtraag.