Function setup_module_loader 

fn setup_module_loader(lua: &Lua, modules_path: &Option<PathBuf>)

Registers a custom require() loader that reads .lua files from the modules directory.

The loader is sandboxed: module names containing .., /, or \ are rejected, so only files directly inside modules_path can be loaded (resolved as <modules_path>/<name>.lua). When modules_path is None, no require is installed. Note: modules are re-evaluated on every require; results are not cached.