fix: class 方法/访问器/constructor/prototype 属性描述符（非枚举/只读），新增 DEFINE_PROP_ATTRS/DEFINE_ACCESSOR_ATTRS

- opcode.rs/inst.rs/contract.rs/vm.rs/vm_dispatch_ctrl.rs：新增两个带 attrs 扩展字的 define 指令
  （attrs bit0=writable, bit1=enumerable, bit2=configurable，与 PropAttributes 一致）
- class/method.rs：方法与非计算访问器改按规范非枚举安装（DefineMethod 语义）
- class/prototype.rs：proto.constructor 非枚举；ctor.prototype 三标志全 false（MakeConstructor）
- 效果：language/statements/class 1782 pass/948 fail -> 1910 pass/716 fail（+128/-232）

crates/oxide_vm/src/vm.rs

@@ -1459,6 +1459,20 @@ impl Vm {
                     self.dispatch_define_global_prop(rd, a, b)?;
                 }
 
+
+                OpCode::DEFINE_PROP_ATTRS => {
+                    let attrs = self.bytecode[self.pc] as u8;
+                    self.pc += 1;
+                    self.dispatch_define_prop_attrs(rd, a, b, attrs)?;
+                }
+
+                OpCode::DEFINE_ACCESSOR_ATTRS => {
+                    let key_word = self.bytecode[self.pc];
+                    let attrs = self.bytecode[self.pc + 1] as u8;
+                    self.pc += 2;
+                    self.dispatch_define_accessor_attrs(rd, a, b, key_word, attrs)?;
+                }
+
                 OpCode::RETURN => match self.dispatch_return(rd) {
                     Ok(Some(result)) => return Ok(result),
                     Ok(None) => {}