Verify SetExtApple::exclude_from_history behaves correctly on upcoming macOS 26

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macOS 26 (currently in developer beta 1) introduces an clipboard history system built into Spotlight.

As it records a history of items put onto the pasteboard, developers who currently use exclude_from_history today for third-party clipboard managers very likely want the same to happen with the new OS feature too.

My preliminary testing using the hello_world example of arboard in a VM indicates that Apple's history manager appears to be respecting the existing functionality for not recording clipboard contents. However this is only observed behavioral testing and reverse engineering, not official documentation, so it can't be relied upon.

Note: this is not a promise from me that this will continue to behave securely. Apple's closed-source code in Spotlight could be updated at any time in the future. Asking to be excluded from history is and always will be a hint.

I've made an official feedback request/radar to Apple to document this properly under FB18123173.