Fix DNS preference continuation leak

[offyotto]

Summary

• fixes the SWIFT TASK CONTINUATION MISUSE: loadFromPreferences() leaked its continuation log by avoiding the ambiguous async preference wrapper
• adds a guarded continuation box for DNS proxy preference load/save operations
• adds a 10-second timeout with a useful entitlement/provisioning error instead of leaving Apply/Revert suspended forever
• ignores late callbacks after timeout so continuations cannot be resumed twice

Notes

The other logs in the report (AppleLanguages, linkd.autoShortcut, tab indexing, task name port) appear to be framework or runtime noise from macOS/SwiftPM app launching rather than Locale-owned code paths. This PR fixes the app-owned continuation leak that can hang DNS proxy preference updates.

Validation

• swift test
• ./script/build_and_run.sh --build-only on the original branch before cherry-picking this focused fix

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Retain the timeout operation until it fires

When loadFromPreferences/saveToPreferences never invoke or retain the completion handler, the only reference left to PreferenceOperationContinuation is this weak capture, so it can be deallocated before the 10-second deadline and the timeout block returns without resuming the checked continuation. That leaves Apply/Revert suspended and preserves the continuation leak in exactly the entitlement/provisioning failure path this change is trying to handle; the timeout closure needs to keep the operation alive until it either fires or an earlier callback clears the continuation.

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