dev: is cython used at run time? at all?

[asarhaddon]

Hello.
Cython is listed in setup.cfg and requirements.txt.
Automated tools building the Debian package deduce the run-time dependencies from them.
Cython does not seem to be used at all, but even if it is, it is most probably only useful at build time.
Could it be removed from these lists and handled separately, like the dependencies for tests?
Thanks.