Keep lambda parameters on one line and parenthesize the body if it expands (#21385)

## Summary

This PR makes two changes to our formatting of `lambda` expressions:
1. We now parenthesize the body expression if it expands
2. We now try to keep the parameters on a single line

The latter of these fixes #8179:

Black formatting and this PR's formatting:

```py
def a():
    return b(
        c,
        d,
        e,
        f=lambda self, *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            *args, **kwargs
        ),
    )
```

Stable Ruff formatting

```py
def a():
    return b(
        c,
        d,
        e,
        f=lambda self,
        *args,
        **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs),
    )
```

We don't parenthesize the body expression here because the call to
`aaaa...` has its own parentheses, but adding a binary operator shows
the new parenthesization:

```diff
@@ -3,7 +3,7 @@
         c,
         d,
         e,
-        f=lambda self, *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
-            *args, **kwargs
-        ) + 1,
+        f=lambda self, *args, **kwargs: (
+            aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs) + 1
+        ),
     )
```

This is actually a new divergence from Black, which formats this input
like this:

```py
def a():
    return b(
        c,
        d,
        e,
        f=lambda self, *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            *args, **kwargs
        )
        + 1,
    )
```

But I think this is an improvement, unlike the case from #8179.

One other, smaller benefit is that because we now add parentheses to
lambda bodies, we also remove redundant parentheses:

```diff
 @pytest.mark.parametrize(
     "f",
     [
-        lambda x: (x.expanding(min_periods=5).cov(x, pairwise=True)),
-        lambda x: (x.expanding(min_periods=5).corr(x, pairwise=True)),
+        lambda x: x.expanding(min_periods=5).cov(x, pairwise=True),
+        lambda x: x.expanding(min_periods=5).corr(x, pairwise=True),
     ],
 )
 def test_moment_functions_zero_length_pairwise(f):
```

## Test Plan

New tests taken from #8465 and probably a few more I should grab from
the ecosystem results.

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_formatter/src/statement/stmt_assign.rs

@@ -9,6 +9,7 @@ use crate::comments::{
     Comments, LeadingDanglingTrailingComments, SourceComment, trailing_comments,
 };
 use crate::context::{NodeLevel, WithNodeLevel};
+use crate::expression::expr_lambda::ExprLambdaLayout;
 use crate::expression::parentheses::{
     NeedsParentheses, OptionalParentheses, Parentheses, Parenthesize, is_expression_parenthesized,
     optional_parentheses,
@@ -18,6 +19,7 @@ use crate::expression::{
     maybe_parenthesize_expression,
 };
 use crate::other::interpolated_string::InterpolatedStringLayout;
+use crate::preview::is_parenthesize_lambda_bodies_enabled;
 use crate::statement::trailing_semicolon;
 use crate::string::StringLikeExtensions;
 use crate::string::implicit::{
@@ -303,12 +305,7 @@ impl Format<PyFormatContext<'_>> for FormatStatementsLastExpression<'_> {
                     && format_implicit_flat.is_none()
                     && format_interpolated_string.is_none()
                 {
-                    return maybe_parenthesize_expression(
-                        value,
-                        *statement,
-                        Parenthesize::IfBreaks,
-                    )
-                    .fmt(f);
+                    return maybe_parenthesize_value(value, *statement).fmt(f);
                 }
 
                 let comments = f.context().comments().clone();
@@ -586,11 +583,7 @@ impl Format<PyFormatContext<'_>> for FormatStatementsLastExpression<'_> {
                             space(),
                             operator,
                             space(),
-                            maybe_parenthesize_expression(
-                                value,
-                                *statement,
-                                Parenthesize::IfBreaks
-                            )
+                            maybe_parenthesize_value(value, *statement)
                         ]
                     );
                 }
@@ -1369,3 +1362,32 @@ fn is_attribute_with_parenthesized_value(target: &Expr, context: &PyFormatContex
         _ => false,
     }
 }
+
+/// Like [`maybe_parenthesize_expression`] but with special handling for lambdas in preview.
+fn maybe_parenthesize_value<'a>(
+    expression: &'a Expr,
+    parent: AnyNodeRef<'a>,
+) -> MaybeParenthesizeValue<'a> {
+    MaybeParenthesizeValue { expression, parent }
+}
+
+struct MaybeParenthesizeValue<'a> {
+    expression: &'a Expr,
+    parent: AnyNodeRef<'a>,
+}
+
+impl Format<PyFormatContext<'_>> for MaybeParenthesizeValue<'_> {
+    fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
+        let MaybeParenthesizeValue { expression, parent } = self;
+
+        if is_parenthesize_lambda_bodies_enabled(f.context())
+            && let Expr::Lambda(lambda) = expression
+            && !f.context().comments().has_leading(lambda)
+        {
+            parenthesize_if_expands(&lambda.format().with_options(ExprLambdaLayout::Assignment))
+                .fmt(f)
+        } else {
+            maybe_parenthesize_expression(expression, *parent, Parenthesize::IfBreaks).fmt(f)
+        }
+    }
+}