gh-117142: ctypes: Migrate global vars to module state

[neonene]

Separated PR from #117181, keeping global state access:

• Move global variables into the global state
• Call functions with the global state attached

I think almost all diffs can be checked mechanically by C compilers except stylistic changes at 9342336.

Unfixed global variables:

File / Func	Var name	Possible fix
malloc_closure.c Py_ffi_closure_alloc() Py_ffi_closure_free()	free_list	Move to module-state or thunk type-state, used by: _ctypes_alloc_callback() CThunkObject_dealloc()
malloc_closure.c	_pagesize	Reload DLL if necessary
cfield.c _ctypes_get_fielddesc()	initialized	Reload DLL if necessary
cfield.c _ctypes_get_fielddesc()	formattable	Reload DLL if necessary
callbacks.c Call_GetClassObject()	context (unreachable)	Do not intern (unused str?)
callbacks.c Call_CanUnloadNow()	context (unreachable)	Do not intern (unused str?)

• Issue: Convert _ctypes extension module to multi-phase init #117142