`SerializeDefaults` option should be assignable on a class-level

For example:

```py
@dataclass
@SerializeDefaults(False)
class ObjectMetadata:
    """
    Kubernetes object metadata.
    """

    name: str
    namespace: str | None = None
    labels: dict[str, str] | None = None
    annotations: dict[str, str] | None = None
```