feat: Begin rewriting tests

[spotandjake]

This is just a draft as I'm not sure we are going to want to merge this work, and I'm not finished writing the implementation.

I noticed that we are not testing a bunch of the binaryen api, and while we do not care too much about testing behaviour as binaryen does that downstream, we probably want to be calling every function to ensure that our api is correct.

This is an effort to rewrite our test suite to cover every function.

Notes:

• I decided to use reasonML over OCaml as it makes reading the code a little nicer.
  • We can easily format it to OCaml if we don't like it.
• I am also documenting the binaryen api as I go (I'll move these changes out into a separate pr once I am done).
• I wanted to use rely, but I can't as it's not available on opam for our opam tests, so instead I just made a little helper framework to make splitting the tests up into unit tests a little nicer.
• I am trying to test things individually to help with understanding what is failing and why, rather than the 2 module approach we previously had, where it could be hard to tell why something changed exactly.

Closes: #244