feat: lots of optimization

* allocate vm stack on the stack
* use Rc instead of Arc
* optimize recursive attribute set

src/bytecode.rs

@@ -37,8 +37,8 @@ pub enum OpCode {
 
     /// push an empty attribute set onto stack
     AttrSet,
-    /// push an empty recursive attribute set onto stack
-    RecAttrSet,
+    /// finalize the recursive attribute set at TOS
+    FinalizeRec,
     /// [ .. set value ] consume 1 element, push a static kv pair (`name`, `value`) into `set`
     PushStaticAttr { name: EcoString },
     /// [ .. set name value ] consume 2 elements, push a dynamic kv pair (`name`, `value`) in to `set`