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/HISTORY

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+Current version is 2.5
+
+* Changes since version 2.4
+  + io and string libraries are now based on pattern matching;
+    the old libraries are still available for compatibility
+  + dofile and dostring can now return values (via return statement)
+  + better support for 16- and 64-bit machines
+  + expanded documentation, with more examples
+
+* Changes since version 2.2
+  + external compiler creates portable binary files that can be loaded faster
+  + interface for debugging and profiling
+  + new "getglobal" fallback
+  + new functions for handling references to Lua objects
+  + new functions in standard lib
+  + only one copy of each string is stored
+  + expanded documentation, with more examples
+
+* Changes since version 2.1
+  + functions now may be declared with any "lvalue" as a name
+  + garbage collection of functions
+  + support for pipes
+
+* Changes since version 1.1
+  + object-oriented support
+  + fallbacks
+  + simplified syntax for tables
+  + many internal improvements