This introduces a tiny alternative to our stdlib, that can be used for testing the interpreter. There are 2 main advantages of such a solution:
1. Performance: on my machine, `runtime-with-intstruments/test` drops from 146s to 65s, while `runtime/test` drops from 165s to 51s. >6 mins total becoming <2 mins total is awesome. This alone means I'll drink less coffee in these breaks and will be healthier.
2. Better separation of concepts – currently working on a feature that breaks _all_ enso code. The dependency of interpreter tests on the stdlib means I have no means of incremental testing – ALL of stdlib must compile. This is horrible, rendered my work impossible, and resulted in this PR.
