refactor: merge GcRoot & Vm

fix/src/lib.rs

@@ -87,8 +87,7 @@ impl Evaluator {
     ) -> Result<fix_common::Value> {
         let root = self.downgrade(source, extra_scope)?;
         let ip = fix_codegen::compile_bytecode(root.as_ref(), self);
-        let vm = Vm::new(self, ip, force_mode);
-        vm.run()
+        Vm::run(self, ip, force_mode)
     }
 
     pub fn add_binding(