test: cover SAMVG runtime artifacts

[rasros]

Summary

• add a fixed-image, supplied-mask SAMVG SVG regression test
• add a scheduled/manual self-hosted GPU workflow that builds and installs the optional CUDA wheel
• run renderer tests and one deterministic CUDA timing step against that built artifact

Validation

• ruff check for new Python files
• pytest tests/refine/test_samvg_regression.py -q

No model downloads, CUDA builds, benchmarks, or full-suite runs were performed locally.