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/jit/dis_mipsel.lua

@@ -0,0 +1,17 @@
+----------------------------------------------------------------------------
+-- LuaJIT MIPSEL disassembler wrapper module.
+--
+-- Copyright (C) 2005-2026 Mike Pall. All rights reserved.
+-- Released under the MIT license. See Copyright Notice in luajit.h
+----------------------------------------------------------------------------
+-- This module just exports the little-endian functions from the
+-- MIPS disassembler module. All the interesting stuff is there.
+------------------------------------------------------------------------------
+
+local dis_mips = require((string.match(..., ".*%.") or "").."dis_mips")
+return {
+  create = dis_mips.create_el,
+  disass = dis_mips.disass_el,
+  regname = dis_mips.regname
+}
+