The window state outlived winit's event loop, which disconnects the Wayland
display when run_app returns. Dropping the state afterwards made the
Wayland clipboard's worker thread destroy its proxies on the freed
display (wl_proxy_destroy in smithay-clipboard), so every quit on GNOME
and KDE Wayland ended in SIGSEGV. The state now drops in exiting(),
while the connection is still open. Reproduced and verified on Fedora
Silverblue 44 (GNOME 50) and Kinoite 44 (Plasma 6.6), x86_64.

Fixes #54.

Assisted-by: claude-opus-5.5