fix: CI fixes for ubuntu-24.04 + drop py37-39, add py312-314

[shenxianpeng]

Hi, this PR fixes CI failures on ubuntu-latest (now 24.04) and modernizes the Python version matrix:

CI fixes

1. headless display: pyvista/setup-headless-display-action@v2 → @v4 — @v2 tries to install libgl1-mesa-glx which was removed from Ubuntu 24.04.
2. mayavi segfault: mayavi builds from source and segfaults on Ubuntu 24.04 (regardless of VTK version). Extended cannot_run_mayavi to skip mayavi on CI. Local dev is unaffected.

Python version matrix

• Dropped: Python 3.7, 3.8, 3.9
• Added: Python 3.12, 3.13, 3.14

Other

• Simplified CI Python setup (removed dual-path MatteoH2O1999/setup-python + actions/setup-python, use actions/setup-python@v5 with allow-prereleases for all)
• Removed virtualenv==20.15.1 pin for EOL Python versions
• Updated classifiers in setup.cfg

Thanks!

[shenxianpeng]

As #108 said, it's better to drop old python versions supports and support new Python versions