refactor: run Lathe, Temper and Knurl as tracked modules

Add a Tracked trait and a Lookahead harness to common-dsp. Each engine is
now its tracker plus a module that follows note events aligned with its
input, so the same module can run behind a shared tracker.

Lathe and Temper output is bit-exact against the old engines. Knurl's
interpolation now reads one newer sample inside the module, so its
latency is one sample longer; the output matches within float rounding.

Each editor exposes body() and toggles() besides show(), so another
editor can draw a module's page.

plugins/lathe/ui/src/lib.rs

@@ -285,6 +285,13 @@ pub fn show(ui: &mut egui::Ui, settings: &mut Settings, state: &mut State) {
         }
         caption(ui, "PITCH FROM");
     });
+    body(ui, settings, state);
+    ui.separator();
+    ui.label(RichText::new(&state.help).color(MUTED));
+}
+
+/// Everything under the header: the standalone editor and Forge both draw it.
+pub fn body(ui: &mut egui::Ui, settings: &mut Settings, state: &mut State) {
     ui.add_space(6.);
     let frame = state.analyzer;
     ui.horizontal_top(|ui| {
@@ -304,8 +311,6 @@ pub fn show(ui: &mut egui::Ui, settings: &mut Settings, state: &mut State) {
         ui.set_width(ui.available_width());
         ui.vertical(|ui| controls(ui, settings, state));
     });
-    ui.separator();
-    ui.label(RichText::new(&state.help).color(MUTED));
 }
 const TOP: f32 = 330.;
 
@@ -429,3 +434,6 @@ fn controls(ui: &mut egui::Ui, settings: &mut Settings, state: &mut State) {
             "Output trim.");
     });
 }
+
+/// Header switches besides Bypass and the pitch source: none here.
+pub fn toggles(_: &mut egui::Ui, _: &mut Settings) {}