Add more detail to `IncompatibleTrait` error

[obycode]

Opening an issue to track Jude's review comment here:

It doesn't have to be done in this PR, but it might be helpful for downstream consumers like Clarinet to know a bit more detail about why these traits are incompatible: it could be because an argument had an incompatible type with the trait definition, the return type was incompatible with the trait definition, or a required function implementation was missing.