[red-knot] Simplify some traits in ast_ids.rs

[AlexWaygood]

Summary

Another small cleanup I'm splitting out from the branch I have locally working towards #13933. The traits HasScopedUseId and HasScopedAstId don't need to be generic: for both traits, the Id associated type is the same for all implementations of the trait. We can remove some complexity here by removing the associated types and specifying concrete types in the trait definitions rather than associated types.

Test Plan

cargo test -p red_knot_python_semantic

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

The traits were generic because we used to have many different AstIds, more than just use and expressions.

I do think removing the associated types makes sense if we only have two ids. An alternative design would be to unify the two traits instead, and use the associated type to differentiate between the different ids.