Treat comments on open parentheses in return annotations as dangling (#6413)

## Summary

Given:

```python
def double(a: int) -> ( # Hello
    int
):
    return 2*a
```

We currently treat `# Hello` as a trailing comment on the parameters
(`(a: int)`). This PR adds a placement method to instead treat it as a
dangling comment on the function definition itself, so that it gets
formatted at the end of the definition, like:

```python
def double(a: int) -> int:  # Hello
    return 2*a
```

The formatting in this case is unchanged, but it's incorrect IMO for
that to be a trailing comment on the parameters, and that placement
leads to an instability after changing the grouping in #6410.

Fixing this led to a _different_ instability related to tuple return
type annotations, like:

```python
def zrevrangebylex(self, name: _Key, max: _Value, min: _Value, start: int | None = None, num: int | None = None) -> (  # type: ignore[override]
):
    ...
```

(This is a real example.)

To fix, I had to special-case tuples in that spot, though I'm not
certain that's correct.

crates/ruff_python_formatter/src/statement/stmt_function_def.rs

@@ -61,17 +61,20 @@ impl FormatNodeRule<StmtFunctionDef> for FormatStmtFunctionDef {
         write!(f, [item.parameters.format()])?;
 
         if let Some(return_annotation) = item.returns.as_ref() {
-            write!(
-                f,
-                [
-                    space(),
-                    text("->"),
-                    space(),
-                    optional_parentheses(
-                        &return_annotation.format().with_options(Parentheses::Never)
-                    )
-                ]
-            )?;
+            write!(f, [space(), text("->"), space()])?;
+            if return_annotation.is_tuple_expr() {
+                write!(
+                    f,
+                    [return_annotation.format().with_options(Parentheses::Never)]
+                )?;
+            } else {
+                write!(
+                    f,
+                    [optional_parentheses(
+                        &return_annotation.format().with_options(Parentheses::Never),
+                    )]
+                )?;
+            }
         }
 
         write!(