Refactor ReadResult decoding for Swift 6

[mickael-menu]

Splits the Streamable.readAsX() async functions into an async read() and synchronous asX() functions. This is to avoid crossing isolation contexts with non sendable objects such as [String: Any].

[Copilot]

Pull request overview

This PR refactors the ReadResult decoding API for Swift 6 compatibility by splitting async reading from synchronous decoding operations. The refactoring addresses Swift 6's stricter concurrency requirements by avoiding crossing isolation contexts with non-Sendable types like [String: Any].

Changes:

• Split Streamable.readAsX() async functions into separate read() (async) and asX() (synchronous) methods on ReadResult<Data> and ReadResult<Data?>
• Made XML parsing methods synchronous (except for file I/O in open(file:) which uses Task.detached)
• Added comprehensive tests for the new ReadResult decoding API using Swift Testing framework
• Updated all call sites across the codebase to use the new read().asX() pattern
• Deprecated the old readAsX() methods with migration guidance

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Tests/SharedTests/Toolkit/Data/ReadResultTests.swift	New comprehensive test suite for ReadResult decoding methods using Swift Testing framework
Tests/SharedTests/Publication/Services/Positions/PositionsServiceTests.swift	Updated to use read().asString() pattern
Tests/SharedTests/Publication/PublicationTests.swift	Updated to use read().asString() pattern
Sources/Streamer/Parser/Readium/ReadiumWebPubParser.swift	Refactored to use read().asRWPM() pattern, moved extension from Streamable to ReadResult<Data>
Sources/Streamer/Parser/Readium/ReadiumGuidedNavigationService.swift	Updated to use read().asJSONObject() pattern
Sources/Shared/Toolkit/XML/XML.swift	Made open(data:) and open(string:) synchronous; open(file:) uses Task.detached for async I/O
Sources/Shared/Toolkit/Format/Sniffers/RPFFormatSniffer.swift	Updated to use read().asJSONObject() pattern
Sources/Shared/Toolkit/Format/Sniffers/EPUBFormatSniffer.swift	Updated to use read().asString() pattern and removed await from synchronous XML parsing
Sources/Shared/Toolkit/Format/FormatSnifferBlob.swift	Removed await from synchronous XML parsing call
Sources/Shared/Toolkit/Data/Streamable.swift	Deprecated readAsString(), readAsJSON(), and readAsJSONObject() with migration messages
Sources/Shared/Toolkit/Data/Resource/ResourceContentExtractor.swift	Updated to use read().asString() and made XML parsing synchronous
Sources/Shared/Toolkit/Data/ReadResult.swift	New file with decode(), asString(), asJSON(), asJSONObject(), and asXML() methods for both ReadResult<Data> and ReadResult<Data?>
Sources/Shared/Toolkit/Data/ReadError.swift	Moved ReadResult typealias to ReadResult.swift
Sources/Shared/Publication/Services/Positions/PositionsService.swift	Updated to use read().asJSONObject() pattern
Sources/Shared/Publication/Services/Content/Iterators/HTMLResourceContentIterator.swift	Updated to use read().asString() pattern
Sources/LCP/Toolkit/ReadResult.swift	Refactored readAsLCPL() from Streamable extension to asLCPL() on ReadResult<Data>

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