fix: guard GhosttyNSView screen observers against stale delivery (mechanism 2, part 2) - #259
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…istration Ports the #258 stale-notification generation guard to GhosttyNSView's windowObserver/screenParametersObserver, the one sibling that didn't get it. removeObserver does not cancel a block already handed to the main queue, so a block enqueued against a torn-down registration batch could still fire after viewDidMoveToWindow re-registered for a new window — reaching the notification.object as? NSWindow downcast against freed state. Forensic match: 5/6 reland-gate minidumps traced to this exact mechanism. windowObserverGeneration bumps on teardown (viewDidMoveToWindow) and deinit; each closure captures its generation at registration and no-ops before doing any work if the instance has since moved on.
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What this does
Completes the stale-notification hardening from #258. Gate forensics on the re-land found the residual crasher: 5/6 new minidumps byte-identical to the mechanism-2 signature, and the only unguarded sibling of the fixed pattern is GhosttyNSView's windowObserver/screenParametersObserver — same queue:.main registration, re-registered on every viewDidMoveToWindow, no generation guard. The evidence pins it precisely: one fault address decodes to ASCII 'New Term' (window-title memory), and the handler's notification.object as? NSWindow downcast requires exactly the objc_retain-of-freed-object that is frame 0 in four dumps.
Ports the identical generation-guard pattern from GhosttySurfaceScrollView (#258): generation captured at registration, bumped on teardown/re-registration and deinit, checked before anything else in both closures — before the downcast that crashes.
Test plan