fix(topola-egui): Always clamp `dt` to `i.predicted_dt`

`egui` clamps its `i.stable_dt` to `i.predicted_dt` only when egui
requested a repaint during the last frame. I however sometimes
experience severe stuttering, which means that this detection
method is insufficient to ensure smoothness. So, let's clamp `dt` to
`i.predicted_dt` and see if this helps.

crates/topola-egui/src/viewport.rs

@@ -55,7 +55,13 @@ impl Viewport {
                                 menu_bar.multilayer_autoroute_options.planar.principal_layer,
                             ),
                             pointer_pos: latest_point,
-                            dt: ctx.input(|i| i.stable_dt),
+                            dt: ctx.input(|i| {
+                                if i.stable_dt <= i.predicted_dt {
+                                    i.stable_dt
+                                } else {
+                                    i.predicted_dt
+                                }
+                            }),
                         };
 
                         workspace.advance_state_by_dt(