kcfg/show: return Digraph directly from KCFGShow.dot

Author: ehildenb

src/pyk/kcfg/show.py

@@ -396,7 +396,7 @@ def to_rule(edge: KCFG.Edge, *, claim: bool = False) -> KRuleLike:
 
         return res_lines
 
-    def dot(self, kcfg: KCFG, node_printer: Callable[[CTerm], Iterable[str]] | None = None) -> str:
+    def dot(self, kcfg: KCFG, node_printer: Callable[[CTerm], Iterable[str]] | None = None) -> Digraph:
         def _short_label(label: str) -> str:
             return '\n'.join(
                 [
@@ -446,7 +446,7 @@ def _short_label(label: str) -> str:
                 attrs = {'class': 'target', 'style': 'solid'}
                 graph.edge(tail_name=node.id, head_name=target_id, label='  false', **attrs)
 
-        return graph.source
+        return graph
 
     def dump(
         self,