Handle and work around concurrency warnings

[Miiha]

Summary by CodeRabbit

• Chores
  • Updated Swift toolchain requirement to version 6.0
  • Upgraded continuous integration to macOS 15 with Xcode 16.4
  • Improved simulator testing with more flexible device matching patterns
  • Enhanced notification API with thread-safety and concurrency attributes

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Walkthrough

The PR upgrades the Swift package to Swift 6.0 tooling, updates CI to macOS 15 with Xcode 16.4, modernizes build device matching in the Makefile, and adds comprehensive Sendable conformance and concurrency attributes across the public API surface. Test discovery manifests for non-Objective-C environments are removed.

Changes

Cohort / File(s)	Change Summary
CI & Build Infrastructure .github/workflows/ci.yml, Makefile, Package.swift	Updates GitHub Actions workflow to macOS 15 with Xcode 16.4; replaces hard-coded device identifiers with regex patterns and changes UDID selection from JSON/jq parsing to grep/sort/head/awk; bumps Swift tools version to 6.0
Concurrency & Sendable Conformance Sources/ComposableUserNotifications/Interface.swift, Sources/ComposableUserNotifications/LiveKey.swift, Sources/ComposableUserNotifications/Model.swift	Adds @preconcurrency imports, Sendable conformance to public types and enums, @Sendable closure annotations on all public closure-typed properties, and wraps completion handlers with UncheckedSendable; marks internal delegate as final Sendable
Test Discovery Removal Tests/ComposableUserNotificationsTests/ComposableUserNotificationsTests.swift, Tests/ComposableUserNotificationsTests/XCTestManifests.swift	Removes allTests static declaration and Linux XCTest manifest entry function for automatic test discovery

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant UserNotificationClient
    participant Delegate
    participant UNUserNotificationCenter

    Note over Client,UNUserNotificationCenter: With Sendable Conformance
    Client->>UserNotificationClient: Call @Sendable closure property
    activate UserNotificationClient
    UserNotificationClient->>Delegate: Route through AsyncStream (UncheckedSendable)
    activate Delegate
    Delegate->>UNUserNotificationCenter: Invoke UserNotifications API
    activate UNUserNotificationCenter
    UNUserNotificationCenter-->>Delegate: Response
    deactivate UNUserNotificationCenter
    rect rgba(200, 150, 100, 0.1)
        Delegate->>Delegate: Wrap completion handler in @Sendable
    end
    Delegate-->>UserNotificationClient: Yield result
    deactivate Delegate
    UserNotificationClient-->>Client: Return async value
    deactivate UserNotificationClient

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~60 minutes

• Model.swift: Dense concurrency refactoring with Sendable conformance across 10+ types; nonisolated(unsafe) rawValue properties and wrapped @Sendable closures require careful verification of thread-safety assumptions
• Interface.swift: Extensive public API surface changes with @Sendable attributes on all closure-typed properties; @preconcurrency imports need validation
• LiveKey.swift: UncheckedSendable wrapping of completion handlers and delegate lifecycle management; verify AsyncStream termination closure correctness
• Makefile: Regex-based device pattern changes and UDID selection logic shift from JSON to grep/awk pipeline; test against various simulator configurations

Poem

🐰 Swift six arrives with Sendable grace, Closures don thread-safe embrace, No more allTests, tests auto-find, macOS 15, Xcode—we're redesigned! Concurrency crowned, our notifs now race, Safe in the cloud, at any pace ✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title Check	✅ Passed	The title "Handle and work around concurrency warnings" accurately describes the primary focus of this changeset. The core substantive changes—across Interface.swift, LiveKey.swift, and Model.swift—center on adding concurrency safety through Sendable conformance, @Sendable closure attributes, @preconcurrency imports, and UncheckedSendable workarounds. While the PR also includes supporting changes (CI workflow update to macOS 15/Xcode 16.4, Makefile device identifier updates, Swift tools version bump to 6.0, and test infrastructure cleanup), these align with or enable the concurrency work. The title is specific enough that a teammate reviewing history would clearly understand this PR addresses concurrency warnings and safety concerns in the composable-user-notifications library.

✨ Finishing touches

• [ ] 📝 Generate docstrings

🧪 Generate unit tests (beta)

• [ ] Create PR with unit tests
• [ ] Post copyable unit tests in a comment
• [ ] Commit unit tests in branch task/concurrency-warnings

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[Miiha]

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