feat: 生成器基础支持（YIELD 帧快照挂起/恢复 + GeneratorPrototype next/return/throw）

- 新增 YIELD/SUSPEND_BODY opcode；function* 识别与 yield emit
- GeneratorState 全量快照 VM 执行上下文（regs/pc/bytecode/spill/save/try/cell 栈段/迭代器）
- 调用时参数初始化（默认值/解构副作用与异常在 g() 时刻生效）
- %GeneratorPrototype%/%GeneratorFunction.prototype% 内建对象与 next/return/throw
- session GC trace 生成器状态 JsValues；闭包捕获分析补 yield/赋值目标扫描

crates/oxide_ir/src/lower.rs

@@ -89,6 +89,7 @@ pub fn lower(f: &IRFunction) -> Result<CompiledModule, String> {
         is_class_constructor: f.is_class_constructor,
         is_derived_constructor: f.is_derived_constructor,
         needs_home_object: f.needs_home_object,
+        is_generator: f.is_generator,
         upvalue_captures: f.upvalue_captures.clone(),
         cells_needed: f.cells_needed,
         flat_id: 0,