gh-159437: Skip unnecessary GC finalizer scans

[mfalco-oai]

With this optimization the GIL collector records pending finalizers while preparing weakref callbacks. If neither finalizers nor callbacks are pending, it skips the finalizer scan. Callbacks and DEBUG_COLLECTABLE keep the full path because they can run Python.

• Issue: Avoid redundant garbage collector traversals #159437

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[pablogsal]

The callback refactor seems bigger than skipping this scan needs. There is a new helper with a long argument list and the caller now has to choose between different garbage lists.

A related change I made in an earlier PR already tracks whether Python may have run. I tried extending that flow by recording pending finalizers during the weakref scan. That was a much smaller change in gc.c and kept the existing callback handling.

Let's keep the existing callback and resurrection flow unless there is a separate application benefit from the larger refactor.

Let's see what @nascheme thinks about the callback refactor too.

[pablogsal]

This fails on its own with -X lazy_imports=all. I tried it with and without the PR and hit the collected object count assertion in each case. Binding patch_stderr = unittest.mock.patch.object before the initial collection fixed the failure. We should do that before this cleanup and use the bound function below.