[Build] Validate Swift 6 library compilation

[NachoSoto]

Summary

• rebase this PR directly onto master after the Swift Testing migration landed
• configure AsyncImageView package targets for Swift 6 with -disable-dynamic-actor-isolation
• document the flag as a workaround for Incorrect actor isolation assumption across Swift 5/6 module boundary leads to dispatch_assert_queue crashes swiftlang/swift#75453
• add an Xcode 26.6 SwiftPM iOS-simulator library build to CI
• make render data and image content modes Sendable
• isolate UIKit rendering to the main actor and preserve scheduler behavior
• use @preconcurrency for the Swift 5 ReactiveSwift boundary, avoiding nonisolated(unsafe) storage and unchecked boxes

CI reproduction

Commit 82dfc96 contains the Swift 6 configuration and CI gate before the production fix. Build and Test run 30112895900 fails in both jobs with the same downstream diagnostic:

static property 'defaultMode' is not concurrency-safe because non-'Sendable' type 'ImageInflaterRendererContentMode' may have shared mutable state

Commit b7769e4 fixes that failure and the subsequent renderer, scheduler, and deinitializer concurrency errors in this same PR. Commit e0636d5 incorporates review feedback by replacing the explicit ReactiveSwift escape hatches with @preconcurrency imports.

Validation

• Build and Test run 30113461493: Swift 6 compatibility build, iOS Simulator test suite, and SwiftLint passed
• local SwiftPM iOS-simulator library build in Swift 6 mode with dynamic actor isolation disabled
• local full iOS Simulator test suite
• swiftlint --config .swiftlint.yml --strict
• git diff --check

Dependencies

None. The previous test-only commit was superseded by merged PR #88, so this PR is now based directly on master.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep unsafe flags out of the published library target

When AsyncImageView is consumed through a versioned SwiftPM dependency rather than built as the root package, SwiftPM rejects the product with the target 'AsyncImageView' in product 'AsyncImageView' contains unsafe build flags. The new CI job builds the repository directly, so it does not exercise this downstream-package restriction. Pass this compiler workaround from the CI build invocation instead of attaching it to the library target.

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