Image Trace: a library colour changed meanwhile makes a background trace stale, and running traces keep frames coming

From the review of #4605. TraceParams::swatches isn't in the settings' JSON (serde skip), so a Document Library trace whose swatches were edited while it ran still applied, with the old colours; the trace's inputs now hold them. The 100 ms repaint that keeps background work moving left traces out, so without input a finished trace could wait for the next event.

crates/ui-egui/src/app.rs

@@ -298,6 +298,7 @@ impl VectorcraftApp {
             || !self.opening.pending.is_empty()
             || !self.plugin_runs.running.is_empty()
             || !self.placing.pending.is_empty()
+            || !self.trace_runs.running.is_empty()
         {
             // Keep the status bar's progress moving and pick the result up when it arrives.
             ctx.request_repaint_after(std::time::Duration::from_millis(100));