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

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

packages/generational-box/tests/reference_counting.rs

@@ -38,7 +38,7 @@ fn move_reference_in_place() {
         let original_owner = S::owner();
         // insert data into the store
         let original = original_owner.insert_rc(data1.clone());
-        let mut reference = original_owner.insert_reference(original).unwrap();
+        let reference = original_owner.insert_reference(original).unwrap();
         // The reference should point to the original value
         assert_eq!(&*reference.read(), &data1);