Support SVG transform angle units

[moreaki]

What changed

Fixes #2735.

This adds SVG angle parsing for transform functions that take angles, so values such as rotate(90deg), rotate(.25turn), rotate(1.5708rad), and skew(20deg) are treated as angles instead of lengths.

Why

Generated SVGs commonly use explicit angle units in CSS transforms. Mermaid Gantt diagrams, for example, emit rules such as transform: rotate(45deg) scale(...) for milestones and rotate(90deg) for rotated tick labels. WeasyPrint previously parsed transform arguments as lengths before dispatching by transform function, which made angle units fail.

Tests

• python -m pytest tests/draw/svg/test_transform.py -q
• python -m pytest tests/draw/svg -q

[liZe]

Thanks a lot for this pull request. 🙏

Here’s a small list of comments, that’s only minor changes.

[moreaki]

Thanks again for the careful review! I’ve addressed the angle-unit feedback in c2f8813f: angle parsing now uses ANGLE_TO_RADIANS and returns radians, rotate/skew consume radians directly, and the SVG transform test is now parametrized across deg, grad, rad, and turn.

[liZe]

Thanks.