math/py-scikit-fem: Add py-scikit-fem 8.1.0

scikit-fem is a pure Python library for performing finite element assembly. Its
main purpose is the transformation of bilinear forms into sparse matrices and
linear forms into vectors.

The library

• has minimal dependencies
• contains no compiled code
• supports one-dimensional, triangular, quadrilateral, tetrahedral and hexahedral finite elements
• includes special elements such as Raviart-Thomas, Nedelec, MINI, Crouzeix-Raviart, Argyris, ...