Remove suite body tracking from SemanticModel (#5848)

## Summary

The `SemanticModel` currently stores the "body" of a given `Suite`,
along with the current statement index. This is used to support "next
sibling" queries, but we only use this in exactly one place -- the rule
that simplifies constructs like this to `any` or `all`:

```python
for x in y:
    if x == 0:
        return True
return False
```

Instead of tracking the state, we can just do a (slightly more
expensive) traversal, by finding the node within its parent and
returning the next node in the body.

Note that we'll only have to do this extremely rarely -- namely, for
functions that contain something like:

```python
for x in y:
    if x == 0:
        return True
```

crates/ruff_python_ast/src/lib.rs

@@ -15,6 +15,7 @@ pub mod statement_visitor;
 pub mod stmt_if;
 pub mod str;
 pub mod token_kind;
+pub mod traversal;
 pub mod types;
 pub mod typing;
 pub mod visitor;