In the free-threaded build, avoid data races caused by updating typeslots or type flags after the type was initially created.  For those(typically rare) cases, use the stop-the-world mechanism.  Remove theuse of atomics when reading or writing type flags.  The use of atomicsis not sufficient to avoid races (since flags are sometimes read withouta lock and without atomics) and are no longer required.

To avoid deadlocks while the world is stopped, we need to avoid calling APIslike _PyObject_HashFast() and _PyDict_GetItemRef_KnownHash().  Collect theslot updates to be done and then apply them all at once.  This reduces theamount of code running in the stop-the-world condition.

Now that stop-the-world is used to do the slot update, these testsare a lot slower in the free-threaded build.  Test with fewer items,which will still hopefully be enough to find bugs in the specializer.

The clearing of Py_TPFLAGS_HAVE_VECTORCALL must be done when the worldis stopped too.

Since we stack allocate one chunk, we need to check 'n' to see if thereare actually any updates to make.  It's pretty common that no updatesare actually needed.

If the two mutex form of the critical section is used, need to put theother mutex into '_cs_mutex'.

This test gets a bit slower, due to stop-the-world but it is not sodramatic.

The apply_slot_updates_world_stopped() name implies that the worldis already stopped, based on convention.  Rename for clarity.