Enhance docs for adj/pred/succ methods in PyDiGraph and add find_successor_node_by_edge method (#1401)

* Add examples to adj/successor/predecessor methods of digraph

* Add find_successor_node_by_edge method

Author: eumiro

releasenotes/notes/add-method-find-successor-node-by-edge-2c14e3f96c61fc8d.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    Added new function: :func:`~find_successor_node_by_edge`
+    to the ``rustworkx.PyDiGraph`` class.
+    This function finds an arbitrary successor node that is connected
+    by an edge that matches given condition.

rustworkx/rustworkx.pyi

@@ -1424,6 +1424,7 @@ class PyDiGraph(Generic[_S, _T]):
     def find_successors_by_edge(
         self, node: int, filter_fn: Callable[[_T], bool], /
     ) -> list[_S]: ...
+    def find_successor_node_by_edge(self, node: int, predicate: Callable[[_T], bool], /) -> _S: ...
     @staticmethod
     def from_adjacency_matrix(
         matrix: npt.NDArray[np.float64], /, null_value: float = ...