gh-117783: Immortalize objects that use deferred reference counting (#118112)

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.

Lib/test/test_functools.py

@@ -1833,6 +1833,7 @@ class TestLRU:
             return 1
         self.assertEqual(f.cache_parameters(), {'maxsize': 1000, "typed": True})
 
+    @support.suppress_immortalization()
     def test_lru_cache_weakrefable(self):
         @self.module.lru_cache
         def test_function(x):