fix: Vm 增加 Drop 收尾释放全部 session 堆数据消除逐实例泄漏

test262 每测试新建 Vm 直接 drop，此前对象堆数据/串/BigInt/cell 全部
泄漏。新增 teardown 收尾函数（epoch+session 对象堆数据、串、BigInt、
cell 统一释放）供 full_reset 与 Drop 共用。连带补齐 promote 分支的
ArrayBuffer 字节缓冲深拷贝（与 sweep 对齐，消除共享所有权 double-free），
并修正依赖旧泄漏行为跨 Vm 解析字符串的 error 测试。

crates/oxide_vm/tests/builtins_error_tests.rs

@@ -16,6 +16,14 @@ fn eval(source: &str) -> Result<JsValue, String> {
     vm.run(&module)
 }
 
+/// 在既有 Vm 内编译执行：结果字符串须在同一 Vm 上下文解析（session 串随 Vm 释放）。
+fn eval_in(vm: &mut Vm, source: &str) -> Result<JsValue, String> {
+    let allocator = oxide_parser::Allocator::default();
+    let program = oxide_parser::parse(&allocator, source).map_err(|e| format!("Parse: {:?}", e))?;
+    let module = Compiler::new().compile(&program).map_err(|e| format!("Compile: {}", e))?;
+    vm.run(&module)
+}
+
 #[test]
 fn error_constructor_creates_object() {
     let mut vm = make_vm();
@@ -286,24 +294,24 @@ fn error_to_string_basic() {
 
 #[test]
 fn error_to_string_empty_message() {
-    let result = eval("new Error().toString()").unwrap();
-    let vm = make_vm();
+    let mut vm = make_vm();
+    let result = eval_in(&mut vm, "new Error().toString()").unwrap();
     let s = vm.lookup_str(result);
     assert_eq!(s, Some("Error".to_string()));
 }
 
 #[test]
 fn error_to_string_type_error() {
-    let result = eval("new TypeError('bad').toString()").unwrap();
-    let vm = make_vm();
+    let mut vm = make_vm();
+    let result = eval_in(&mut vm, "new TypeError('bad').toString()").unwrap();
     let s = vm.lookup_str(result);
     assert_eq!(s, Some("TypeError: bad".to_string()));
 }
 
 #[test]
 fn error_to_string_name_only() {
-    let result = eval("Error.prototype.toString.call({name: 'E'})").unwrap();
-    let vm = make_vm();
+    let mut vm = make_vm();
+    let result = eval_in(&mut vm, "Error.prototype.toString.call({name: 'E'})").unwrap();
     let s = vm.lookup_str(result);
     assert_eq!(s, Some("E".to_string()));
 }
@@ -355,16 +363,16 @@ fn error_stack_is_string() {
 
 #[test]
 fn error_stack_starts_with_header() {
-    let result = eval("new Error().stack()").unwrap();
-    let vm = make_vm();
+    let mut vm = make_vm();
+    let result = eval_in(&mut vm, "new Error().stack()").unwrap();
     let s = vm.lookup_str(result).unwrap();
     assert!(s.starts_with("Error"), "stack should start with 'Error', got: {}", s);
 }
 
 #[test]
 fn error_stack_frame_format() {
-    let result = eval("(function foo() { return new Error('boom').stack(); })()").unwrap();
-    let vm = make_vm();
+    let mut vm = make_vm();
+    let result = eval_in(&mut vm, "(function foo() { return new Error('boom').stack(); })()").unwrap();
     let s = vm.lookup_str(result).unwrap();
     assert!(s.contains("    at "), "stack should have 4-space indent, got: {}", s);
 }

crates/oxide_vm/tests/generator_gc_tests.rs

@@ -18,8 +18,10 @@ fn compile(source: &str) -> oxide_bytecode::module::CompiledModule {
 #[test]
 fn generator_promoted_to_global_survives_full_reset_cleanly() {
     let mut vm = Vm::new();
-    vm.run(&compile("function* g(){ yield 1; yield 2; } globalThis.it = g(); globalThis.it.next(); 0"))
-        .expect("run1");
+    vm.run(&compile(
+        "function* g(){ yield 1; yield 2; } globalThis.it = g(); globalThis.it.next(); 0",
+    ))
+    .expect("run1");
     assert!(vm.session_object_count() > 0, "生成器挂 global 应被 promote 进 session");
 
     // global 含 session 对象即强制重建：旧 global 丢弃、it 槽不存在，全程无悬垂访问
@@ -31,6 +33,8 @@ fn generator_promoted_to_global_survives_full_reset_cleanly() {
     let text = vm.lookup_str(result).expect("typeof 应返回字符串").to_string();
     assert_eq!(text, "undefined");
     // 新会话可正常创建并推进生成器。
-    let ok = vm.run(&compile("function* h(){ yield 9; } var it2 = h(); it2.next().value")).expect("run3");
+    let ok = vm
+        .run(&compile("function* h(){ yield 9; } var it2 = h(); it2.next().value"))
+        .expect("run3");
     assert_eq!(format!("{ok}"), "9");
 }