nodecore: 3³ optical T-flipflop

basically the [frequency halver](https://spectra.video/w/rce7KY7bNvynXq2GBZcDej) without the complication of sending the input signal "through" in addition to changing state. (the original behaviour can still be replicated by simply attaching an edge detection to the state output.) each time the input signal turns on, the internal binary state gets toggled.