toplevel: store containing float

src/tree/containing.rs

@@ -1,5 +1,5 @@
 use {
-    crate::tree::{Node, ToplevelNode, WorkspaceNode},
+    crate::tree::{FloatNode, Node, ToplevelNode, WorkspaceNode},
     std::rc::Rc,
 };
 
@@ -37,4 +37,7 @@ pub trait ContainingNode: Node {
     fn cnode_set_pinned(self: Rc<Self>, pinned: bool) {
         let _ = pinned;
     }
+    fn cnode_get_float(self: Rc<Self>) -> Option<Rc<FloatNode>> {
+        None
+    }
 }