fix(common): Node.map_clear should have return type annotation Any (

#8564)

Previously `Node.map_clear` had a `dict` return type annotation, just as
`Node.map`, even though the main rationale behind `map_clear` is that it
returns only the result of the root node and discards all the
intermediaries.

ibis/common/graph.py

@@ -264,9 +264,7 @@ def map(self, fn: Callable, filter: Optional[Finder] = None) -> dict[Node, Any]:
         return results
 
     @experimental
-    def map_clear(
-        self, fn: Callable, filter: Optional[Finder] = None
-    ) -> dict[Node, Any]:
+    def map_clear(self, fn: Callable, filter: Optional[Finder] = None) -> Any:
         """Apply a function to all nodes in the graph more memory efficiently.
 
         Alternative implementation of `map` to reduce memory usage. While `map` keeps