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/snapshots/ruff_python_parser__parser__tests__named_expression.snap

@@ -0,0 +1,36 @@
+---
+source: crates/ruff_python_parser/src/parser.rs
+expression: parse_ast
+---
+NamedExpr(
+    ExprNamedExpr {
+        range: 1..15,
+        target: Name(
+            ExprName {
+                range: 1..2,
+                id: "x",
+                ctx: Store,
+            },
+        ),
+        value: BinOp(
+            ExprBinOp {
+                range: 8..13,
+                left: Name(
+                    ExprName {
+                        range: 8..9,
+                        id: "y",
+                        ctx: Load,
+                    },
+                ),
+                op: Mult,
+                right: Name(
+                    ExprName {
+                        range: 12..13,
+                        id: "z",
+                        ctx: Load,
+                    },
+                ),
+            },
+        ),
+    },
+)