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.

docs/knurl/CHANGELOG.md

@@ -1,5 +1,10 @@
 # Knurl changelog
 
+## Unreleased
+
+- The engine is now a module that also runs inside Forge. The sound is
+  unchanged; the latency is one sample longer.
+
 ## 0.2.0
 
 - Change the CLAP ID to `io.narl.bass-foundry.knurl`. Hosts see this as a new