GLib.Cancellable timeout configuration in Vala async methods
Goal is to configure cooperative cancellation and timeouts for Vala async methods that accept GLib.Cancellable. Vala exposes Cancellable as a first-class async parameter from GIO/GObject bindings. Timeouts are typically built with GLib.Timeout.add or GLib.Source and manually wired to Cancellable.cancel(). Cancellation is cooperative; the callee must poll can