Working version of keyboard with variable lengths; tests and cleanup

test/runtime.mjs

@@ -131,6 +131,10 @@ const midin = () => {
   return (ccNum) => strudel.ref(() => 0); // returns ref with default value 0
 };
 
+const keyboard = async () => {
+  return () => strudel.silence;
+};
+
 const sysex = ([id, data]) => {};
 
 // TODO: refactor to evalScope
@@ -150,6 +154,7 @@ evalScope(
   */
   {
     midin,
+    keyboard,
     sysex,
     // gist,
     // euclid,