feature: improve load times for large notes

[AnthonyMcDougal]

Large multi-page notes take a while (~30 sec? depending on length) to load, and this repeats every time the file is selected for the open pane.

1. Is there a way to decrease this time?
2. Is there a way to not repeat this every time the file is selected, or is exporting the image the only way?

[philips]

Yeah unfortunately parsing the images is slow. I am sure there is a way to speed that up but I don’t know when I would have time to dig into that.

If someone were want to take a performance pass at the library the file is in here https://github.com/philips/supernote-typescript/blob/main/src/conversion.ts

[philips]

Added generation of a cpuprofile to one of the tests to start to hunt this down: philips/supernote-typescript@57f19b7

[philips]

I just merged #44 which reduces parsing of a 10 page file from 7s to about 1.5s for me. Please try out the beta release for 2.4.0 via BRAT. I would appreciate your testing.