Decouple from Roblox scripting environment

[grilme99]

Jest Lua is currently coupled to Roblox's scripting APIs. It should be decoupled, and all environment-specific usage should be moved into jest-environment-* packages.

[westurner]

Would lemur be useful or necessary for this?

I forked LPGhatguy/lemur to create a wally.toml for lemur, haven't yet pushed a package to wally-index with the patch to support *.client.lua and *.server.lua[u]?. https://github.com/westurner/lemur