anyrender_svg: render text from usvg's layouted glyphs instead of flattened paths

[nicoburns]

Summary

anyrender_svg previously rendered usvg::Node::Text by recursing into text.flattened(), i.e. drawing text as pre-converted vector paths. This PR switches it to consume text.layouted() and submit real glyph runs via PaintScene::draw_glyphs, so backends receive actual font/glyph data (enabling hinting, glyph caching, etc.).

New text module (crates/anyrender_svg/src/text.rs), feature-gated behind the existing text feature (the flattened() fallback remains when the feature is off):

• TextRenderer loads faces from the tree's fontdb::Database (Binary/File/SharedFile sources) into anyrender::FontData, cached per fontdb::ID along with units_per_em and axis info (via skrifa).
• For each usvg::layout::Span: draws overline/underline before glyphs and line-through after (matching resvg's paint order), honoring span.visible and fill/stroke paint_order.
• Glyphs whose PositionedGlyph::transform() is a pure translate+uniform-scale (font_size/upem) are batched into runs of anyrender::Glyph { id, x, y }; runs flush on font or variation-coordinate changes. Rotated/skewed glyphs (e.g. textPath) are drawn as single-glyph runs with the glyph transform folded into the run transform.
• Font variations: span font_variations plus automatic opsz (when FontOpticalSizing::Auto and the font has an opsz axis) are normalized through skrifa's axis mapping and passed as NormalizedCoords.
• Since draw_glyphs takes no brush transform, gradient brush transforms are baked into the gradient geometry (apply_brush_transform), including a correction for single-glyph runs whose run transform differs from text space.

Also adds skrifa = "0.44" as an optional workspace dependency and extends the text feature with usvg/memmap-fonts + usvg/system-fonts.

Verified with a vello_cpu test harness rendering plain, underlined, gradient fill+stroke, rotated, and text-on-a-path SVGs:

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/2dde303678964855b869f1254e8858e5
Requested by: @nicoburns

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