Fix subscriptions for read only signals passed as props (#3173)

* add a fuzzing test for reference counted generational boxes

* Fix subscriptions for readonlysignal passed as props

* Don't subscribe to dropped contexts

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/generational-box/src/lib.rs

@@ -145,7 +145,7 @@ impl<T, S: Storage<T>> GenerationalBox<T, S> {
     }
 
     /// Change this box to point to another generational box
-    pub fn point_to(&mut self, other: GenerationalBox<T, S>) -> BorrowResult {
+    pub fn point_to(&self, other: GenerationalBox<T, S>) -> BorrowResult {
         S::change_reference(self.raw, other.raw)
     }
 }