feat: 迭代器原型基建：%IteratorPrototype% 链 + 各集合迭代器原型

新增 %IteratorPrototype%（含 @@iterator 返回自身，经原型链被全部迭代器
继承，it[Symbol.iterator]() === it 恒等）与 %ArrayIteratorPrototype%/
%MapIteratorPrototype%/%SetIteratorPrototype%/%StringIteratorPrototype%/
%RegExpStringIteratorPrototype%（链到 %IteratorPrototype%）；Array/Map/Set/
TA/String/matchAll 迭代器包装统一挂对应原型；补 Array/String 的 @@iterator
别名绑定。集合迭代器原型不含 return 方法（规范集合迭代器无 return）。

crates/oxide_vm/src/bindings/mod.rs

@@ -380,6 +380,19 @@ fn bind_iterator_global(core: &Arc<KernelCore>, session: &KernelSession, global:
         &[("from", oxide_builtins::iterator::iterator_from::<crate::vm::Vm> as *const (), 1)],
     );
     bind_existing_global(core, global, "Iterator", JsValue::from_js_object(Box::into_raw(iterator)));
+
+    // %IteratorPrototype% 自身可迭代（@@iterator 返回 this，经原型链被全部集合迭代器继承）。
+    let iter_proto_ptr = session.builtin_world().iterator_proto.as_ptr() as *mut JsObject;
+    let iter_proto = unsafe { &mut *iter_proto_ptr };
+    bind_well_known_method(
+        session.builtin_world(),
+        core,
+        iter_proto,
+        0,
+        "iterator",
+        oxide_builtins::iterator::iterator_symbol_iterator::<crate::vm::Vm> as *const (),
+        0,
+    );
 }
 
 fn bind_stub_globals(core: &Arc<KernelCore>, session: &KernelSession, global: &mut JsObject) {