Expand NamedExpr range to include full range of parenthesized value (#6632)

## Summary

Given:

```python
if (
    x
    :=
    (  # 4
        y # 5
    )  # 6
):
    pass
```

It turns out the parser ended the range of the `NamedExpr` at the end of
`y`, rather than the end of the parenthesis that encloses `y`. This just
seems like a bug -- the range should be from the start of the name on
the left, to the end of the parenthesized node on the right.

## Test Plan

`cargo test`

crates/ruff_python_parser/src/parser.rs

@@ -603,6 +603,13 @@ def func[T, U: str, *Ts, **P]():
         insta::assert_debug_snapshot!(parse_ast);
     }
 
+    #[test]
+    fn test_named_expression() {
+        let source = "(x := ( y * z ))";
+        let parse_ast = parse_expression(source, "<test>").unwrap();
+        insta::assert_debug_snapshot!(parse_ast);
+    }
+
     #[test]
     fn test_with_statement() {
         let source = "\