gh-104090: Add exit code to multiprocessing ResourceTracker (GH-115410)

This builds on https://github.com/python/cpython/pull/106807, which adds
a return code to ResourceTracker, to make future debugging easier.
Testing this “in situ” proved difficult, since the global ResourceTracker is
involved in test infrastructure. So, the tests here create a new instance and
feed it fake data.

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Co-authored-by: Yonatan Bitton <yonatan.bitton@perception-point.io>
Co-authored-by: Yonatan Bitton <bityob@gmail.com>
Co-authored-by: Antoine Pitrou <antoine@python.org>