fix: missing `type_traits` include

Usage of `std::is_trivially_constructible` in `defs.hpp` requires including `type_traits`. This missing include leads to errors about that type not being found when building with clang++-22 with libc++-22.

include/godot_cpp/core/defs.hpp

@@ -32,6 +32,7 @@
 
 #include <cstddef>
 #include <cstdint>
+#include <type_traits>
 #include <utility>
 
 namespace godot {