Add support for SVG covers

[grighakobian]

Summary

This pull request addresses the SVG covers are not supported issue.

Known limitation

The SVG rendering uses CGSVGDocument CoreGraphics functions loaded dynamically via dlsym. While these are stable since iOS 13 and widely used, they are not part of the public API. A future iteration could replace this with a third-party SVG parsing library (e.g. SVGKit) or a WebKit snapshot approach for full public API compliance.

[mickael-menu]

Thank you @grighakobian! Using CoreSVG is smart, I was going to implement it with WebKit. It's a private API but it seems reasonable:
https://github.com/SDWebImage/SDWebImageSVGCoder?tab=readme-ov-file#note-for-coresvg-framework

[Copilot]

Pull request overview

This PR adds SVG cover support to the publication cover pipeline by rendering SVG resources into UIImage, and extends the default cover selection logic to consider SVG links in the manifest (including reading order and alternates). It also introduces fixture data and tests to validate SVG cover behavior.

Changes:

• Add UIImage.fromSVG(_:maxSize:) to render SVG data into a bitmap using dynamically-loaded CoreGraphics SVG symbols.
• Update ResourceCoverService to load SVG covers (explicit .cover, reading order, alternates) and support sizing via coverFitting(maxSize:).
• Add SVG cover fixtures and extend cover service test coverage for SVG scenarios.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Sources/Shared/Toolkit/Extensions/UIImage.swift	Adds SVG-to-bitmap rendering helper used by cover loading.
Sources/Shared/Publication/Services/Cover/ResourceCoverService.swift	Extends cover selection/loading to support SVG and size-aware loading.
Tests/SharedTests/Publication/Services/Cover/CoverServiceTests.swift	Adds tests validating SVG cover selection and scaling behavior.
Tests/SharedTests/Fixtures/Publication/Services/cover-svg.svg	Adds an SVG fixture used by new tests.

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[mickael-menu]

Thanks a lot @grighakobian!