curved attribute not supported in edge

My understanding is that the 'curved' attribute is not supported in Edge,
Apparently this can be corrected by adding it to
```python
@property
def style_attributes(self) -> List[str]:
"""The style attributes to add to the style tag in the XML

Returns:
list: A list of style attributes
"""
return [
"rounded",
"curved",
"sketch",
"shadow",
"flowAnimation",
```

and adding
```python
self.curved: Optional[int] = kwargs.get("curved", None)
```
in the `__init__` of `Edge`, but I do not know the library well so maybe I missed something.

Start with Edge.__init__ and the style_attributes property shown in the issue, then inspect how Edge attributes are serialized into Draw.io XML. Confirm that a curved edge can be constructed and that the generated XML includes both the curved attribute and its style name.

Written by the indexing model from the issue text.