The package needs porting to Python 3.13.
Fixed with commit 4b60e11271ab6cfde9e31e904b18fb837521bacb Author: Alexey Shvetsov <alexxy@gentoo.org> Date: Wed Apr 2 12:10:55 2025 +0300 sci-chemistry/gromacs: enable py3.13 Signed-off-by: Alexey Shvetsov <alexxy@gentoo.org>