copy Graph should return Self (#1441)

Author: zen-xu

rustworkx/rustworkx.pyi

@@ -1240,7 +1240,7 @@ class PyGraph(Generic[_S, _T]):
         /,
         weight_combo_fn: Callable[[_T, _T], _T] | None = ...,
     ) -> int: ...
-    def copy(self) -> PyGraph[_S, _T]: ...
+    def copy(self) -> Self: ...
     def degree(self, node: int, /) -> int: ...
     def edge_index_map(self) -> EdgeIndexMap[_T]: ...
     def edge_indices(self) -> EdgeIndices: ...
@@ -1398,7 +1398,7 @@ class PyDiGraph(Generic[_S, _T]):
         check_cycle: bool | None = ...,
         weight_combo_fn: Callable[[_T, _T], _T] | None = ...,
     ) -> int: ...
-    def copy(self) -> PyDiGraph[_S, _T]: ...
+    def copy(self) -> Self: ...
     def edge_index_map(self) -> EdgeIndexMap[_T]: ...
     def edge_indices(self) -> EdgeIndices: ...
     def edge_indices_from_endpoints(self, node_a: int, node_b: int) -> EdgeIndices: ...