Updating the chart is slow for large datasets

We have to display large datasets in combination with relatively complex tooltips. This results in chart options which are very large in JSON format (browser console says ~ 2.5 MB of JSON that is passed to Highcharts).
I know that there are several techniques to improve performance for large datasets and we try to stick to the best practices. I think the main issue with the flutter implementation is the conversion step from dart objects to JSON to whatever Highcharts itself is doing with the JSON.

I assume that it's not really possible to circumvent the JSON conversion, but the main problem here is that it all happens synchronously.

This means, when we pass such a big dataset to Highcharts, the UI is blocked for 1-2 seconds.
I think making the chart updates asynchronous would be a nice improvement!

Begin with the Flutter chart-update path that converts Dart objects to JSON before passing options to Highcharts. Profile the conversion and update flow with a large dataset and complex tooltips, then determine how asynchronous updates can avoid blocking the UI. Done means large updates no longer block the UI for 1–2 seconds while preserving chart behavior.

Written by the indexing model from the issue text.