Fix zulip unstable formatting with end-of-line comments (#6386)

## Bug

Given
```python
x = () - (#
)
```
the comment is a dangling comment of the empty tuple. This is an
end-of-line comment so it may move after the expression. It still
expands the parent, so the operator breaks:
```python
x = (
    ()
    - ()  #
)
```
In the next formatting pass, the comment is not a trailing tuple but a
trailing bin op comment, so the bin op doesn't break anymore. The
comment again expands the parent, so we still add the superfluous
parentheses
```python
x = (
    () - ()  #
)
```

## Fix

The new formatting is to keep the comment on the empty tuple. This is a
log uglier and again has additional outer parentheses, but it's stable:
```python
x = (
    ()
    - (  #
    )
)
```

## Alternatives

Black formats all the examples above as
```python
x = () - ()  #
```
which i find better. 

I would be happy about any suggestions for better solutions than the
current one. I'd mainly need a workaround for expand parent having an
effect on the bin op instead of first moving the comment to the end and
then applying expand parent to the assign statement.

crates/ruff_python_formatter/src/builders.rs

@@ -253,6 +253,16 @@ impl<'ast> Format<PyFormatContext<'ast>> for EmptyWithDanglingComments<'_> {
                 self.opening,
                 // end-of-line comments
                 trailing_comments(&self.comments[..end_of_line_split]),
+                // Avoid unstable formatting with
+                // ```python
+                // x = () - (#
+                // )
+                // ```
+                // Without this the comment would go after the empty tuple first, but still expand
+                // the bin op. In the second formatting pass they are trailing bin op comments
+                // so the bin op collapse. Suboptimally we keep parentheses around the bin op in
+                // either case.
+                (!self.comments[..end_of_line_split].is_empty()).then_some(hard_line_break()),
                 // own line comments, which need to be indented
                 soft_block_indent(&dangling_comments(&self.comments[end_of_line_split..])),
                 self.closing