vendor: 引入 Lua 2.5 官方源码 + 移植评估 (lua_2.5 分支)

- 前 lua_State 时代 API, 比 3.2 更原始(无 upvalue/无独立编译)
- 评估结论: 不建议移植(多实例冲突+管道模式不可实现), 见 doc/ADAPTATION-lua25.md
- 建议历史脚本用 5.1 兼容模式运行替代

lib/lua/src/fallback.h

@@ -0,0 +1,37 @@
+/*
+** $Id: fallback.h,v 1.13 1996/04/25 14:10:00 roberto Exp $
+*/
+ 
+#ifndef fallback_h
+#define fallback_h
+
+#include "lua.h"
+#include "opcode.h"
+
+extern struct FB {
+  char *kind;
+  Object function;
+  int nParams;
+  int nResults;
+} luaI_fallBacks[];
+
+#define FB_ERROR  0
+#define FB_INDEX  1
+#define FB_GETTABLE  2
+#define FB_ARITH  3
+#define FB_ORDER  4
+#define FB_CONCAT  5
+#define FB_SETTABLE  6
+#define FB_GC 7
+#define FB_FUNCTION 8
+#define FB_GETGLOBAL 9
+
+void luaI_setfallback (void);
+int luaI_ref (Object *object, int lock);
+Object *luaI_getref (int ref);
+void luaI_travlock (int (*fn)(Object *));
+void luaI_invalidaterefs (void);
+char *luaI_travfallbacks (int (*fn)(Object *));
+
+#endif
+