Traits

Traits describe behavior a type provides. They feel partly like TypeScript interfaces, but implementation is explicit and coherence rules decide where impls may live. Planned exercises: 1. choose trait declaration syntax. 2. recognise impl Trait for Type. 3. choose a trait method receiver. 4. fill a trait method signature. 5. fill an impl block. 6. write a small trait and impl. 7. write a function that accepts a trait bound. 8. translate a TS interface plus class. 9. fix a missing trait import or missing impl error.