Add View.onPreferenceChange

[Dark-Existed]

Implement #925

[augmentcode]

🤖 Augment PR Summary

Summary: This PR implements View.onPreferenceChange (per #925) so views can react to preference value updates.

Changes:

• Introduces onPreferenceChange(_:perform:) on View and a new internal _PreferenceActionModifier to observe a specific PreferenceKey.
• Adds a stateful AttributeGraph binder (PreferenceBinder) that tracks the last observed value, resets across phase resets, and enqueues the user action when the preference changes.
• Uses an UpdateCycleDetector to reduce the risk of feedback loops when an action triggers further updates.
• Adjusts preference-writing scene/view modifiers to avoid mutating the original inputs while still removing the key from child inputs, ensuring writers are created when the ancestor requests the key.
• Adds an example demonstrating .preference + .onPreferenceChange usage.

Technical Notes: Preference change delivery is implemented as a transactional graph attribute that schedules the callback via Update.enqueueAction, mirroring existing “action binder” patterns used elsewhere in the codebase.

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[augmentcode]

Review completed. 1 suggestion posted.

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[augmentcode]

onPreferenceChange is being added as a public API, but it doesn’t appear to carry the @available(OpenSwiftUI_v1_0, *) availability annotation pattern used by other preference APIs (e.g. preference, transformPreference). Consider aligning the availability annotations to keep the public surface/versioning consistent.

Severity: low

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