self.__cpp_transporter__() proof of concept: Enable passing C++ pointers across extensions even if the PYBIND11_INTERNALS_VERSIONs do not match.

tests/test_cpp_transporter.cpp

@@ -0,0 +1,4 @@
+#include "pybind11_tests.h"
+#include "test_cpp_transporter_traveler_bindings.h"
+
+TEST_SUBMODULE(cpp_transporter, m) { pybind11_tests::test_cpp_transporter::wrap_traveler(m); }