More public documentation/guidance on each contract test

We provide a contract for handlers to follow in the docs, but it will be useful for providers to know what each individual test within the contract tests is trying to accomplish, what the inputs are for the test, and what the expected outcome is without having to read through the code of the test. Might also be useful to have more context on the test failures when we're reporting the results as well (ie why it's bad the test is failing, suggestions on how to fix it).