feat: add Lua 5.1 addon system with .toc loader and /run command

Foundation for WoW-compatible addon support:

- Vendor Lua 5.1.5 source as a static library (extern/lua-5.1.5)
- TocParser: parses .toc files (## directives + file lists)
- LuaEngine: Lua 5.1 VM with sandboxed stdlib (no io/os/debug),
  WoW-compatible print() that outputs to chat, GetTime() stub
- AddonManager: scans Data/interface/AddOns/ for .toc files,
  loads .lua files on world entry, skips LoadOnDemand addons
- /run <code> slash command for inline Lua execution
- HelloWorld test addon that prints to chat on load

Integration: AddonManager initialized after asset manager, addons
loaded once on first world entry, reset on logout. XML frame
parsing is deferred to a future step.

extern/lua-5.1.5/src/lmem.c

@@ -0,0 +1,86 @@
+/*
+** $Id: lmem.c,v 1.70.1.1 2007/12/27 13:02:25 roberto Exp $
+** Interface to Memory Manager
+** See Copyright Notice in lua.h
+*/
+
+
+#include <stddef.h>
+
+#define lmem_c
+#define LUA_CORE
+
+#include "lua.h"
+
+#include "ldebug.h"
+#include "ldo.h"
+#include "lmem.h"
+#include "lobject.h"
+#include "lstate.h"
+
+
+
+/*
+** About the realloc function:
+** void * frealloc (void *ud, void *ptr, size_t osize, size_t nsize);
+** (`osize' is the old size, `nsize' is the new size)
+**
+** Lua ensures that (ptr == NULL) iff (osize == 0).
+**
+** * frealloc(ud, NULL, 0, x) creates a new block of size `x'
+**
+** * frealloc(ud, p, x, 0) frees the block `p'
+** (in this specific case, frealloc must return NULL).
+** particularly, frealloc(ud, NULL, 0, 0) does nothing
+** (which is equivalent to free(NULL) in ANSI C)
+**
+** frealloc returns NULL if it cannot create or reallocate the area
+** (any reallocation to an equal or smaller size cannot fail!)
+*/
+
+
+
+#define MINSIZEARRAY	4
+
+
+void *luaM_growaux_ (lua_State *L, void *block, int *size, size_t size_elems,
+                     int limit, const char *errormsg) {
+  void *newblock;
+  int newsize;
+  if (*size >= limit/2) {  /* cannot double it? */
+    if (*size >= limit)  /* cannot grow even a little? */
+      luaG_runerror(L, errormsg);
+    newsize = limit;  /* still have at least one free place */
+  }
+  else {
+    newsize = (*size)*2;
+    if (newsize < MINSIZEARRAY)
+      newsize = MINSIZEARRAY;  /* minimum size */
+  }
+  newblock = luaM_reallocv(L, block, *size, newsize, size_elems);
+  *size = newsize;  /* update only when everything else is OK */
+  return newblock;
+}
+
+
+void *luaM_toobig (lua_State *L) {
+  luaG_runerror(L, "memory allocation error: block too big");
+  return NULL;  /* to avoid warnings */
+}
+
+
+
+/*
+** generic allocation routine.
+*/
+void *luaM_realloc_ (lua_State *L, void *block, size_t osize, size_t nsize) {
+  global_State *g = G(L);
+  lua_assert((osize == 0) == (block == NULL));
+  block = (*g->frealloc)(g->ud, block, osize, nsize);
+  if (block == NULL && nsize > 0)
+    luaD_throw(L, LUA_ERRMEM);
+  lua_assert((nsize == 0) == (block == NULL));
+  g->totalbytes = (g->totalbytes - osize) + nsize;
+  return block;
+}
+