feat(rdp): printer redirection, saved as PostScript

An optional 'Nexus Terminal' printer (IronRDP's PostScript driver
announce) appears on the remote desktop; each job is written to
'Nexus print <time>.ps' in Downloads, with a toast saying where. Jobs
are capped at 256 MiB and empty jobs leave no file. The shared drive and
the printer now share one RDPDR backend (rdp_devices); the printer
works on every platform, the drive on Linux and macOS.

Tested with a unit test driving create/write/close; xrdp has no printer
redirection, so not exercised against a server.

rust/app/src/app.rs

@@ -485,6 +485,7 @@ impl App {
                 }
             }
             Event::Warning { message, .. } => self.s.error(message),
+            Event::Info { message, .. } => self.s.success(message),
             Event::Irc { session, event } => {
                 if let Some(View::Irc(v)) = self.s.panes.get_mut(&session).map(|p| &mut p.view) {
                     v.on_event(event);