refactor: realm 与 Vm 生命周期解耦，Vm 持 Arc<Realm>

crates/oxide_vm/tests/session_arena_tests.rs

@@ -15,7 +15,8 @@ fn run_source(vm: &mut Vm, source: &str) -> JsValue {
 
 fn global_prop(vm: &Vm, name: &str) -> JsValue {
     let si = vm.kernel_core().perm_interner().intern(name).0;
-    let global = vm.session().global_object();
+    let session = vm.session();
+    let global = session.global_object();
     let pos = vm
         .kernel_core()
         .shape_forge()