Type Alias LuaCFunction 

pub type LuaCFunction = fn(&mut LuaState) -> Result<usize, LuaError>;

A Lua-callable function pointer. C: lua_CFunction.

TODO(phase-b): the lua-types crate uses a placeholder LuaCFnPtr = fn() -> i32 since it can’t reference LuaState without a circular dep. The real signature is fn(&mut LuaState) -> Result<usize, LuaError>, kept here as the lua-vm-facing type alias.