fix: for-of/for-in 提前退出时按规范顺序完成 IteratorClose

return/break/continue 逃出 for-of 时此前完全不执行 IteratorClose：
BREAK/CONTINUE/RETURN 指令现在经 ext 字携带词法逃出的迭代器层数
（for-of + for-in 各 16 位），运行时在全部 finally 穿越之后、真正
跳转/返回之前按 LIFO 关闭——与规范 §13.7.5.4（循环体完成值已含
内部 try-finally 处理，IteratorClose 在后）顺序一致。

- emit 词法：LabelCtx 增加 for-of/for-in 深度计数，loop/switch/label
  打开时快照，break/continue/return 按当前深度减目标深度计算逃出层数
  （switch 内 break 以 switch 打开点为基准，目标循环自身不计入）
- 指令编码：brk/cont/ret 三参构造，lower 跳转路径补发 ext 字
- 运行时：dispatch_break/continue/return 读取逃出计数，无 finally 时
  直接关闭后跳转/返回，有 finally 时随 Completion 悬挂由 TRY_FINALLY_END
  在穿越完成后消费；生成器 .return()/.throw() 注入经 complete_generator_return
  全关快照栈迭代器；return() 抛错经 unwind 替代完成值并关闭剩余迭代器
- 顺带：for-in 逃出残留（无 return() 语义，仅弹栈）；for-await-of 的
  异步迭代器不做同步关闭（return() promise 须 await，走异步机制）
- 新增 15 项回归测试：return/labeled break/continue/switch/while/finally
  顺序/抛错优先/生成器注入/for-in/for-await-of 嵌套

crates/oxide_emit/src/stmt/iteration/do_while.rs

@@ -14,7 +14,7 @@ impl Emitter {
         let start_label = ctx.next_label_id();
         let end_label = ctx.next_label_id();
         ctx.labels.set_label_pos(start_label, ctx.insts.len());
-        ctx.push_loop(end_label, start_label);
+        ctx.push_loop(end_label, start_label, crate::emit_ctx::LoopKind::Plain);
         let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
         self.emit_statement(&dw.body, ctx)?;
         let test_reg = self.emit_expression(&dw.test, ctx)?;

crates/oxide_emit/src/stmt/iteration/for_.rs

@@ -40,7 +40,7 @@ impl Emitter {
         let start_label = ctx.next_label_id();
         let update_label = ctx.next_label_id();
         let end_label = ctx.next_label_id();
-        ctx.push_loop(end_label, update_label);
+        ctx.push_loop(end_label, update_label, crate::emit_ctx::LoopKind::Plain);
         let n_labeled = ctx.take_pending_loop_labels(end_label, update_label);
         // 循环头声明中被嵌套函数捕获的 let/const 绑定：每迭代 fresh cell。
         let mut fresh_bindings: Vec<(String, u8)> = Vec::new();

crates/oxide_emit/src/stmt/iteration/for_in.rs

@@ -17,7 +17,7 @@ impl Emitter {
         let obj_reg = self.emit_expression(&fi.right, ctx)?;
         ctx.inst(Inst::new(OpCode::FOR_IN_INIT, Operand::None, Operand::Reg(obj_reg), Operand::None));
         ctx.labels.set_label_pos(start_label, ctx.insts.len());
-        ctx.push_loop(end_label, start_label);
+        ctx.push_loop(end_label, start_label, crate::emit_ctx::LoopKind::ForIn);
         let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
         let done_reg = ctx.alloc_reg();
         ctx.inst(Inst::new(OpCode::FOR_IN_DONE, Operand::Reg(done_reg), Operand::None, Operand::None));

crates/oxide_emit/src/stmt/iteration/for_of.rs

@@ -29,7 +29,7 @@ impl Emitter {
         let iter_src_reg = self.emit_expression(&fo.right, ctx)?;
         ctx.inst(Inst::new(OpCode::FOR_OF_INIT, Operand::None, Operand::Reg(iter_src_reg), Operand::None));
         ctx.labels.set_label_pos(start_label, ctx.insts.len());
-        ctx.push_loop(end_label, start_label);
+        ctx.push_loop(end_label, start_label, crate::emit_ctx::LoopKind::ForOf);
         let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
         let has_reg = ctx.alloc_reg();
         ctx.inst(Inst::new(OpCode::FOR_OF_DONE, Operand::Reg(has_reg), Operand::None, Operand::None));
@@ -64,7 +64,7 @@ impl Emitter {
             Operand::None,
         ));
         ctx.labels.set_label_pos(start_label, ctx.insts.len());
-        ctx.push_loop(end_label, start_label);
+        ctx.push_loop(end_label, start_label, crate::emit_ctx::LoopKind::ForAwaitOf);
         let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
         let next_reg = ctx.alloc_reg();
         ctx.inst(Inst::new(OpCode::FOR_AWAIT_OF_NEXT, Operand::Reg(next_reg), Operand::None, Operand::None));

crates/oxide_emit/src/stmt/iteration/while_loop.rs

@@ -12,7 +12,7 @@ impl Emitter {
         let start_label = ctx.next_label_id();
         let end_label = ctx.next_label_id();
         ctx.labels.set_label_pos(start_label, ctx.insts.len());
-        ctx.push_loop(end_label, start_label);
+        ctx.push_loop(end_label, start_label, crate::emit_ctx::LoopKind::Plain);
         let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
         let test_reg = self.emit_expression(&wh.test, ctx)?;
         ctx.inst(Inst::jmp_if_false(test_reg, end_label));