I think recent changes to SUSHI are taking a performance toll

Recently, I have been experiencing issues where SUSHI takes more than a minute to finish it's work on TWO different projects which have more than a hundred resources each.

This is preventing both of these projects from building with the automatic FHIR IG Builder integration. There's a workaround, which is to rename the FSH folder and run SUSHI first, so not a killer, but rather annoying to have to change build processes and instruct everyone doing a local build to run the processes differently (and yes, I can just change my own build.bat file, so also NOT a big issue).

But it occurs to me that SUSHI, being a JavaScript application, is single threaded, and could benefit from multiple threads for processing multiple resource definitions once it has evaluated the dependencies. I know there's a way to do that in Node.

I'd even take a crack at it, but I just don't know enough about how to build and test a Node.js application yet in Eclipse.

No source file, test, or entry point is named. Start by reproducing the build slowdown on a project with more than 100 resources, compare the normal build with the workaround of renaming the FSH folder, and profile SUSHI to locate the regression; done means the affected builds complete without that workaround and performance is verified.

Written by the indexing model from the issue text.