modernize codebase: es6 upgrade

[jedluhmann]

Refactor code to upgrade to modern ES6 syntax and best practices.
Upgrades include bun, eslint, prettier, mocha, chai, and c8.

[andreyvit]

Hey, thank you, and sorry, but a full rewrite from a new contributor is indistinguishable from a supply chain attack. I agree json-diff needs modernization, but we might not be able to merge this as is, unless other contributors want to take on the verification.

[jedluhmann]

Hi, Andrey. I want to let you know that this is an incredibly beautiful bit of code that you have created. To see such a complex problem solved in such a concise and elegant manner is not only an incredible motivator for me, but also a reminder of everything that I love about software engineering. The same can be said about @ewoudenberg/difflib, which is a very worthy companion.

I find json-diff to be a tremendously useful project and I would like to help contribute in whatever way I can. I have a couple of other changes that I am working on—updating the code is simply the first step as it provides good footing on which to build. The second change is to optimize the code for performance. So far, I'm seeing a 3x boost in performance.

My use case involves generating over 1000 json files programmatically that contain deeply nested JSON, which I think gives me some rather unique insight. The third change will involve bug fixes, which is my primary reason for updating the code and making sure that all of the test cases are in good shape.