Fix: Cycles occasional crash after Metal render

Happens for renders from command line, when kernel specialization
thread is still working after the allocators on the Blender side
have been deinitialized.

Add an explicit deinitializaiton, which ensures all Cycles worker
and cache threads are finished before the allocators are deinitialized.

This should solve occasional crashes when running regression tests
for Metal or Metal-RT.

Pull Request: https://projects.blender.org/blender/blender/pulls/128239

intern/cycles/blender/python.cpp

@@ -35,6 +35,10 @@
 #  include <OSL/oslquery.h>
 #endif
 
+#ifdef WITH_METAL
+#  include "device/metal/device.h"
+#endif
+
 CCL_NAMESPACE_BEGIN
 
 namespace {
@@ -144,6 +148,10 @@ static PyObject *init_func(PyObject * /*self*/, PyObject *args)
 
 static PyObject *exit_func(PyObject * /*self*/, PyObject * /*args*/)
 {
+#ifdef WITH_METAL
+  device_metal_exit();
+#endif
+
   ShaderManager::free_memory();
   TaskScheduler::free_memory();
   Device::free_memory();