Functor and Applicative laws for core library types

[joelberkeley]

Description

The functor and applicative laws for common library types. I am missing some applicative laws for list/snoclist, cos they're non-trivial. I could also add monad laws. I don't know if I'll get round to them (let's assume not). Laws from here https://en.wikibooks.org/wiki/Haskell/Applicative_functors. PLEASE CORRECT ME IF I'VE INTERPRETED THEM WRONG.

This is a draft to get opinions before I invest effort needlessly.

It's quite unclear what types make sense to implement these for. I originally asked about Prelude types, which doesn't include Vect. Unfussed if we include that or not. It's quite hard to know where the line is (what about List1, State etc.).

Could do just the functor laws for now - they're always easy.

Self-check

• This is my first time contributing, I've carefully read CONTRIBUTING.md
  and I've updated CONTRIBUTORS with my name.
• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG_NEXT.md
• I confirm that this contribution did not involve GenerativeAI nor Large Language Models.