gh-117142: Port _ctypes to multi-phase init

[neonene]

An attempt to introduce multi-phase initialization:

• Keep using a global state.

• Integrate CDataType_* functions into CType_Type_*().

• Make module_traverse() visit almost all global variables to invoke module_clear(), leaving aside malloc_closure.c (free_list) for now. The free_list is related to CThunkObject_dealloc() and I'm not sure if it also needs isolation.

@encukou @erlend-aasland @aisk

• Issue: gh-117142