TestResult decorator classes do not have the addDuration method added to TestResult in Python 3.12

[Will]

Python 3.12 added [[https://docs.python.org/3/library/unittest.html#unittest.TestResult.addDuration | an addDuration method]]. The unittest test runner tries to use this method now and triggers a warning if it is not present. I specifically encounter this warning when using stestr which wraps test results with AutoTimingTestResultDectorator (see [[https://github.com/mtreinish/stestr/blob/cc66736df90968126585540b220fea663b124bbf/stestr/subunit_runner/run.py#L44-L45 | here]]). An example of a project where this warning is generated like this is rustworkx. [[https://github.com/Qiskit/rustworkx/actions/runs/7012357436/job/19076767764 | Here]] is a CI log with the warning generated.

A simpler reproducer is to use {{{stestr -t . run test}}} with a test.py file with this content (tested with stestr 4.1.0):

{{{#!python
from unittest import TestCase

class TestExample(TestCase):
    def test_pass(self):
        pass
}}}

[Will (wsha)]

Since there is an overlap of maintainers with testtools, I will mention here that I think classes like ExtendedToStreamDecorator in testtools might also need to add addDuration, but it is less clear to me if those classes are supposed to mirror the unittest.TestResult interface or just work with the testtools classes, so I won't open an issue for them now.