Build a better testing framework.

[AiredaleDev]

Currently I have a bunch of miniscule example programs I run manually. This is very cringe and painful. Something that uses cargo test should be plenty! Maybe as a part of this I'd also build a nicer way to construct ASTs...

[AiredaleDev]

I've made progress on this front but I'm still unsatisfied -- I should not want or need some LLM to translate an AST I have working into a 500-line long unit test for me. This also implies that most parser tests are regression tests (which would make sense considering the nature of what it does.)

I think what I'll do instead is (de)serialize ASTs to JSON, and use the compiler to generate output that is correct (hence regression test). This would make the creation of tests much easier and incentivize me to actually make them!