feat: 适配 LuaJIT 2.1 (luajit_2.1 分支)

- lib/lua 替换为完整 LuaJIT 2.1 仓库(Makefile+src+dynasm, 官方结构)
- 构建系统改造: lib/lua/CMakeLists.txt 改为调用 LuaJIT 自带 make
  (BUILDMODE=static CFLAGS=-fPIC) 产出 libluajit.a; 顶层链接该静态库
  并加 -Wl,-E 导出符号(静态链 LuaJIT 必需)
- 补充 lua.hpp 转发头兼容桥接层 'lua/lua.hpp' include 路径
- 桥接层沿用 5.1 方案: Registry 存 iopath / luaL_tolstring 兜底 /
  typed interop 无 integer 子类型(LUA_VERSION_NUM=501)
- [关键修复] lua_remove 栈越界 bug(各版本共有, LuaJIT 下显性崩溃):
  * unload_lib: ref 记录的是 gettop+1, 实际移除应用 ref-1
  * clean(): 原逐个 remove 循环恒越界且多次移除后索引偏移,
    属死代码(末尾 settop(L,0) 已清栈), 直接删除
  该 bug 在 Lua 5.4 中被隐式容忍, 在 LuaJIT 的 GC finalizer 中
  表现为 lj_gc_finalize_cdata 段错误
- 测试跨版本断言同步(自 5.1.5)
- 验证: GTest 44/44 通过

lib/lua/src/lj_vmevent.h

@@ -0,0 +1,62 @@
+/*
+** VM event handling.
+** Copyright (C) 2005-2026 Mike Pall. See Copyright Notice in luajit.h
+*/
+
+#ifndef _LJ_VMEVENT_H
+#define _LJ_VMEVENT_H
+
+#include "lj_obj.h"
+
+/* Registry key for VM event handler table. */
+#define LJ_VMEVENTS_REGKEY	"_VMEVENTS"
+#define LJ_VMEVENTS_HSIZE	4
+
+#define VMEVENT_MASK(ev)	((uint8_t)1 << ((int)(ev) & 7))
+#define VMEVENT_HASH(ev)	((int)(ev) & ~7)
+#define VMEVENT_HASHIDX(h)	((int)(h) << 3)
+#define VMEVENT_NOCACHE		255
+
+#define VMEVENT_DEF(name, hash) \
+  LJ_VMEVENT_##name##_, \
+  LJ_VMEVENT_##name = ((LJ_VMEVENT_##name##_) & 7)|((hash) << 3)
+
+/* VM event IDs. */
+typedef enum {
+  VMEVENT_DEF(BC,	0x00003883),
+  VMEVENT_DEF(TRACE,	0x12d91467),
+  VMEVENT_DEF(RECORD,	0x1284bf4f),
+  VMEVENT_DEF(TEXIT,	0x129df2b0),
+  VMEVENT_DEF(ERRFIN,	0x12d93888),
+  LJ_VMEVENT__MAX
+} VMEvent;
+
+#ifdef LUAJIT_DISABLE_VMEVENT
+#define lj_vmevent_send(g, ev, args)		UNUSED(g)
+#define lj_vmevent_send_(g, ev, args, post)	UNUSED(g)
+#else
+#define lj_vmevent_send(g, ev, args) \
+  if ((g)->vmevmask & VMEVENT_MASK(LJ_VMEVENT_##ev)) { \
+    lua_State *V = vmthread(g); \
+    ptrdiff_t argbase = lj_vmevent_prepare(V, LJ_VMEVENT_##ev); \
+    if (argbase) { \
+      args \
+      lj_vmevent_call(V, argbase); \
+    } \
+  }
+#define lj_vmevent_send_(g, ev, args, post) \
+  if ((g)->vmevmask & VMEVENT_MASK(LJ_VMEVENT_##ev)) { \
+    lua_State *V = vmthread(g); \
+    ptrdiff_t argbase = lj_vmevent_prepare(V, LJ_VMEVENT_##ev); \
+    if (argbase) { \
+      args \
+      lj_vmevent_call(V, argbase); \
+      post \
+    } \
+  }
+
+LJ_FUNC ptrdiff_t lj_vmevent_prepare(lua_State *L, VMEvent ev);
+LJ_FUNC void lj_vmevent_call(lua_State *L, ptrdiff_t argbase);
+#endif
+
+#endif