Refactor state flow to boost performance

For intervals < ~24ms, the main thread as unable to cope up in handling
worker responses due to Mainframe rendering on each execution. To
resolve this, this commit delegates all execution-time states to child
components, controlled imperatively from Mainframe.

This yields huge performance boost, with main thread keeping up with
worker responses even at interval of 5ms.

ui/execution-controls.tsx

@@ -33,9 +33,9 @@ const IntervalInput = (props: {
   return (
     <div style={styles.inputWrapper}>
       <NumericInput
-        min={20}
+        min={5}
+        stepSize={5}
         defaultValue={20}
-        stepSize={10}
         minorStepSize={null}
         leftIcon="time"
         clampValueOnBlur