dillon1000/react

[be] make evaluator and worker easier to debug in sprout

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jsdom and other libraries seem to cause jest workers to exit with 
`forceExit:true`. Not sure what option I set (or global I've overwritten) but 
console logs aren't flushed as a result, making debugging a bit confusing. 

This PR: 

- Moves some code from `eval(...)` to a typechecked real js function. I always 
had trouble debugging the `eval`ed code, so smaller code snippet is better here. 

- waits for jest workers to end before exiting