graphics/py-visvis: Update to 1.15.0

Mainly a bugfix release, with some modernization.

Changelog: https://github.com/almarklein/visvis/compare/v1.14.0...v1.15.0

Reported by: portscout, Repology
MFH: 2025Q1

(cherry picked from commit 3d1bc41979de3229d97a9bf11dc848e9406b4168)