Avoid omitting optional parentheses for argument-less parentheses (#6484)

## Summary

This PR fixes some misformattings around optional parentheses for
expressions.

I first noticed that we were misformatting this:

```python
return (
    unicodedata.normalize("NFKC", s1).casefold()
    == unicodedata.normalize("NFKC", s2).casefold()
)
```

The above is stable Black formatting, but we were doing:
```python
return unicodedata.normalize("NFKC", s1).casefold() == unicodedata.normalize(
    "NFKC", s2
).casefold()
```

Above, the "last" expression is a function call, so our
`can_omit_optional_parentheses` was returning `true`...

However, it turns out that Black treats function calls differently
depending on whether or not they have arguments -- presumedly because
they'll never split empty parentheses, and so they're functionally
non-useful. On further investigation, I believe this applies to all
parenthesized expressions. If Black can't split on the parentheses, it
doesn't leverage them when removing optional parentheses.

## Test Plan

Nice increase in similarity scores.

Before:

- `zulip`: 0.99702
- `django`: 0.99784
- `warehouse`: 0.99585
- `build`: 0.75623
- `transformers`: 0.99470
- `cpython`: 0.75989
- `typeshed`: 0.74853

After:

- `zulip`: 0.99705
- `django`: 0.99795
- `warehouse`: 0.99600
- `build`: 0.75623
- `transformers`: 0.99471
- `cpython`: 0.75989
- `typeshed`: 0.74853

crates/ruff_python_formatter/src/statement/stmt_assign.rs

@@ -1,6 +1,5 @@
-use ruff_python_ast::{Expr, StmtAssign};
-
 use ruff_formatter::{format_args, write, FormatError};
+use ruff_python_ast::{Expr, StmtAssign};
 
 use crate::context::{NodeLevel, WithNodeLevel};
 use crate::expression::parentheses::{Parentheses, Parenthesize};
@@ -52,7 +51,7 @@ struct FormatTargets<'a> {
 impl Format<PyFormatContext<'_>> for FormatTargets<'_> {
     fn fmt(&self, f: &mut PyFormatter) -> FormatResult<()> {
         if let Some((first, rest)) = self.targets.split_first() {
-            let can_omit_parentheses = has_own_parentheses(first);
+            let can_omit_parentheses = has_own_parentheses(first, f.context()).is_some();
 
             let group_id = if can_omit_parentheses {
                 Some(f.group_id("assignment_parentheses"))