fix(topola-egui): clamp timestep slider to 0.001-3.0 instead of 0.0-3.0

Timestep should never be set to 0 because this freezes the GUI if the
execution takes a long time.

Of course, this solution assumes that any lengthy operation is split
into sufficiently fine steppable steps.

Fixes https://codeberg.org/topola/topola/issues/203

crates/topola-egui/src/menu_bar.rs

@@ -109,7 +109,7 @@ impl MenuBar {
 
                         ui.label(tr.text("tr-menu-view-frame-timestep"));
                         ui.add(
-                            egui::widgets::Slider::new(&mut self.frame_timestep, 0.0..=3.0)
+                            egui::widgets::Slider::new(&mut self.frame_timestep, 0.001..=3.0)
                                 .suffix(" s"),
                         );
                     });