feat: Add typescript declaration files

[Daimywil]

Added *.d.ts files to describe luau code structure so nevermore can be used using roblox-ts. 99% of the types weren handwritten based on the source code. Some unimplemented methods have been left out of the type declarations intentionally.
Also corrects a few missing dependencies in some packages.

Rx

A key difference in rxjs and nevermore Rx is that Rx accepts an array of operators instead of varargs. This wont work with typescript, since it cant infer types in the chain between operators in an array. To tackle this, I choose to type it as varargs of operators, just like rxjs does. This way, types can be automatically inferred throughout the pipe chain. Since the outputted code will be incorrect, a fork of roblox-ts will correct it. I believe the benefit of having operators in the pipe chain fully type-checked far outweigh the cons of needing a fork.