[`ruff`] Fix `RUF033` breaking with named default expressions (#19115)
## Summary
The generated fix for `RUF033` would cause a syntax error for named
expressions as parameter defaults.
```python
from dataclasses import InitVar, dataclass
@dataclass
class Foo:
def __post_init__(self, bar: int = (x := 1)) -> None:
pass
```
would be turned into
```python
from dataclasses import InitVar, dataclass
@dataclass
class Foo:
x: InitVar[int] = x := 1
def __post_init__(self, bar: int = (x := 1)) -> None:
pass
```
instead of the syntactically correct
```python
# ...
x: InitVar[int] = (x := 1)
# ...
```
## Test Plan
Test reproducer (plus some extra tests) have been added to the test
suite.
## Related
Fixes: https://github.com/astral-sh/ruff/issues/18950
ruff
1079975b - [`ruff`] Fix `RUF033` breaking with named default expressions (#19115)
