- Update build workflow to use Node 20.x
- Use webkitAudioContext is AudioContext is not defined
- Use audioCtx.createBuffer in place of new AudioBuffer
- Use createBufferSource in place of new AudioBufferSourceNode
- Fix layout that relied on aspect-ratio, closes #94 

An issue with the sample rate still remains for modspeech.

Changes made to accommodate Safari 13 and 14.

…111)

- Workaround for #110 where we've observed that the sample rate of 19000 isn't supported. We'll aim to increase the sample rate in a separate PR but this will at least mean the simulator isn't put in a bad state.
- Reuse the audio context created after the user interaction, as there are limits to how many you can create on Safari 13 (4 in my BrowserStack testing). I think we always intended to do this, but careful review needed as this is a more significant change than I was anticipating. We already had clean up code for the nodes when the board stops. We never cleaned up the context. So I think we were assuming it lived forever. If this doesn't work out then an alternative is to try closing the old one before creating the new one.