fix: test_factory_constructors.py failure triggered by test_register_duplicate_class (#2564)

* Demonstrate test_factory_constructors.py failure without functional changes from #2335

* Revert "Demonstrate test_factory_constructors.py failure without functional changes from #2335"

This reverts commit ca33a8021fc2a3617c3356b188796528f4594419.

* Fix test crash where registered Python type gets garbage collected

* Clean up some more internal structures when class objects go out of scope

* Reduce length of std::erase_if-in-C++20 comment

* Clean up code for cleaning up type internals

* Move cleaning up of type info in internals to tp_dealloc on pybind11_metaclass