Read clip-path from style and CSS rules, and quoted url() references - #544

get_clippath() only reads the clip-path attribute, and only in the exact form url(#id). So the clip is silently dropped when it comes from:

• a style attribute: style="clip-path: url(#clip)",
• a CSS rule: .cls-2 { clip-path: url(#clip-path); }, as in Illustrator's CSS exports and in svgo-optimized matplotlib charts,
• a quoted or spaced reference: url("#clip"), url('#clip'), url( #clip ), which is how browsers serialize the property.

Gradient fills already accept all of these (_GRADIENT_URL_RE). get_clippath() now applies the style rules to the node first, as the baseline-shift lookup does (clip-path is not inherited, so only the node itself is read), and parses the value with _GRADIENT_URL_RE. clip-path="none" still clips nothing.

Real files: PyMuPDF's docs/images/icons/icon-svg.svg (Illustrator) gets its 1 clip path, and the matplotlib charts in rapidfuzz's documentation (docs/Usage/img/*.svg) get their 18 each; on main they get none, so the plot lines are not clipped to the axes.

Added test_clipping_path_reference (attribute, both quotes, spaces, style, CSS class) and test_clipping_path_none; 5 of the 8 cases fail on main. Added a ### Fixed entry in CHANGELOG.md (I used #545, as I expect #544 for the <image> PR; I'll fix it if needed). pytest (without the network-dependent sample downloads), ruff format --check, ruff check and mypy src tests pass.

AI-assisted (Claude Code); I reviewed and tested the change