feat(execution-engine): Rc-based JSON value (#813)

Use custom JSON value type with Rc inside.  It cannot be edited, but producing new values based on child element is very cheap.

This new type is used exclusively in AquaVM internals.  Interface APIs use serde_json's Value or JSON strings, as before.
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Co-authored-by: raftedproc <71657594+raftedproc@users.noreply.github.com>

crates/testing-framework/src/execution/mod.rs

@@ -690,7 +690,7 @@ mod tests {
     #[test]
     fn test_transformed_shared() {
         struct Service {
-            state: RefCell<std::vec::IntoIter<JValue>>,
+            state: RefCell<std::vec::IntoIter<serde_json::Value>>,
         }
 
         impl MarineService for Service {