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_char.h

@@ -0,0 +1,42 @@
+/*
+** Character types.
+** Donated to the public domain.
+*/
+
+#ifndef _LJ_CHAR_H
+#define _LJ_CHAR_H
+
+#include "lj_def.h"
+
+#define LJ_CHAR_CNTRL	0x01
+#define LJ_CHAR_SPACE	0x02
+#define LJ_CHAR_PUNCT	0x04
+#define LJ_CHAR_DIGIT	0x08
+#define LJ_CHAR_XDIGIT	0x10
+#define LJ_CHAR_UPPER	0x20
+#define LJ_CHAR_LOWER	0x40
+#define LJ_CHAR_IDENT	0x80
+#define LJ_CHAR_ALPHA	(LJ_CHAR_LOWER|LJ_CHAR_UPPER)
+#define LJ_CHAR_ALNUM	(LJ_CHAR_ALPHA|LJ_CHAR_DIGIT)
+#define LJ_CHAR_GRAPH	(LJ_CHAR_ALNUM|LJ_CHAR_PUNCT)
+
+/* Only pass -1 or 0..255 to these macros. Never pass a signed char! */
+#define lj_char_isa(c, t)	((lj_char_bits+1)[(c)] & t)
+#define lj_char_iscntrl(c)	lj_char_isa((c), LJ_CHAR_CNTRL)
+#define lj_char_isspace(c)	lj_char_isa((c), LJ_CHAR_SPACE)
+#define lj_char_ispunct(c)	lj_char_isa((c), LJ_CHAR_PUNCT)
+#define lj_char_isdigit(c)	lj_char_isa((c), LJ_CHAR_DIGIT)
+#define lj_char_isxdigit(c)	lj_char_isa((c), LJ_CHAR_XDIGIT)
+#define lj_char_isupper(c)	lj_char_isa((c), LJ_CHAR_UPPER)
+#define lj_char_islower(c)	lj_char_isa((c), LJ_CHAR_LOWER)
+#define lj_char_isident(c)	lj_char_isa((c), LJ_CHAR_IDENT)
+#define lj_char_isalpha(c)	lj_char_isa((c), LJ_CHAR_ALPHA)
+#define lj_char_isalnum(c)	lj_char_isa((c), LJ_CHAR_ALNUM)
+#define lj_char_isgraph(c)	lj_char_isa((c), LJ_CHAR_GRAPH)
+
+#define lj_char_toupper(c)	((c) - (lj_char_islower(c) >> 1))
+#define lj_char_tolower(c)	((c) + lj_char_isupper(c))
+
+LJ_DATA const uint8_t lj_char_bits[257];
+
+#endif