fix lua package: correct directory, namespace and install

- Move package from packages/l/lua to packages/m/mcpplibs-capi-lua
  (directory must match package name)
- Build only library target to avoid parallel std module conflicts
- Install lua_headers.h for cppm dependency
- Fix test namespace to mcpplibs::capi::lua

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Sunrisepeak

packages/l/lua/xmake.lua packages/m/mcpplibs-capi-lua/xmake.luapackages/l/lua/xmake.lua renamed to packages/m/mcpplibs-capi-lua/xmake.lua

@@ -14,5 +14,7 @@ package("mcpplibs-capi-lua")
     add_deps("lua")
 
     on_install(function (package)
-        import("package.tools.xmake").install(package)
+        local configs = {}
+        import("package.tools.xmake").install(package, configs, {target = "mcpplibs-capi-lua"})
+        os.cp("src/capi/lua_headers.h", package:installdir("include"))
     end)

tests/l/lua/main.cpp

@@ -2,6 +2,8 @@ import std;
 import mcpplibs.capi.lua;
 
 int main() {
+    using namespace mcpplibs::capi;
+
     auto L = lua::L_newstate();
     lua::L_openlibs(L);