Bump blitz to 0.3.0-alpha.4; add DataUrlNetProvider for @font-face; expose StyleThreading

[HenriqueAnzoategui]

Summary

Three pieces, all needed for hyper-render to work against the current blitz release and to be usable in concurrent embedder contexts (servers rendering documents per request via tokio::task::spawn_blocking, batch pre-renderers, etc.):

1. Bump blitz-* = "=0.3.0-alpha.4" (was 0.2). Companion bumps: anyrender 0.10, anyrender_vello_cpu 0.12.1, and the PDF-feature deps krilla 0.7, stylo 0.17, parley 0.9. stylo MUST match blitz's pin (links = "servo_style_crate"). MSRV is now Rust 1.92.

   render_to_png and render_to_pdf now take &mut HtmlDocument — blitz_paint::paint_scene requires a mutable document reference as of alpha.4.

2. DataUrlNetProvider in src/net.rs — an in-process NetProvider resolving data: URIs synchronously. Without it, blitz-dom falls back to DummyNetProvider, which silently drops every embedded asset — that's the historical "system fonts only" / "@font-face not yet supported" limitation. With it, @font-face { src: url(data:font/...) } and inline base64 images load correctly. Non-data: URLs are still ignored; hyper-render does no real network I/O.

3. New Config.style_threading: StyleThreading field that forwards to DocumentConfig.style_threading (introduced in blitz-dom 0.3.0-alpha.4 via dioxuslabs/blitz#437). Defaults to StyleThreading::Parallel, matching blitz's default — no behavior change for existing callers. Pass StyleThreading::Sequential to disable Stylo's global thread pool and make render safe to invoke from many OS threads concurrently.

   StyleThreading is mirrored as a hyper-render-owned enum (same pattern as ColorScheme) with a From impl for the blitz type, so the public API doesn't leak blitz_dom types.

Changes

• Cargo.toml — dep version bumps.
• src/net.rs (new) — DataUrlNetProvider.
• src/config.rs — StyleThreading enum + field on Config + builder method.
• src/lib.rs — wires the net provider and the style-threading field through to DocumentConfig in create_document; flips render_to_png/render_to_pdf to &mut for the new paint_scene signature.
• src/render/png.rs / pdf.rs — &mut HtmlDocument and document.as_mut() for paint_scene.
• tests/font_face.rs (new) — integration test for @font-face with data: URI.
• README.md / CLAUDE.md — lift the @font-face not yet supported bullet.
• CHANGELOG.md — 0.3.0 entry.

Tests

• 4 unit tests in src/net.rs for DataUrlNetProvider: base64, percent-encoded, non-data: ignored, binary payload round-trip.
• tests/font_face.rs: renders HTML with @font-face { src: url(data:font/otf;base64,...) } and asserts a valid PNG comes out.
• Doctest on the new style_threading builder method.

Verified locally

• cargo fmt --all --check ✓
• cargo clippy --no-default-features --features png --all-targets -- -D warnings ✓
• cargo test --no-default-features --features png ✓ (15 passed)
• cargo check --no-default-features --features pdf ✓