Test `Debug` Implementations

Although `Debug` implementations aren't considered stable here ([they aren't in the Rust standard library either](https://doc.rust-lang.org/stable/core/fmt/trait.Debug.html#stability)), it is still a good idea to test to ensure the debug output is as intended.

The main obstacle here will be dealing with the arbitrary internal order of `Archetype`s. There needs to be some way to test the output is correct, even if the order of debug strings is not guaranteed.