Introduce an "AlwaysUnblockProtectedView" setting (default: false, scope: QuickLook.Plugin.OfficeViewer) and use it to skip the confirmation dialog and automatically unblock the ZoneIdentifier for internet-downloaded files. If the setting is false, preserve the existing prompt flow and keep the previous behavior of showing a warning and only unblocking on user confirmation.
Changed all Plugin classes and PluginManager to be sealed, preventing further inheritance. This improves code safety and clarifies the intended usage of these classes.
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