Use stestr again for unittests

With the release of Python 3.12.1 we stopped using stest in CI because
3.12.1 introduced a breaking API change to the unittest runner API that
broke a dependency of stestr, testtools. This has been worked around
with a new testtools release so we can restore using stestr in CI again
which should improve test run throughput. This commit restores using
stestr for the test CI jobs and local runs. The cibuildwheel config
remains unchanged and uses the stdlib unittest runner still, just for
simplicity so we don't need to install additional test dependencies.

.github/workflows/main.yml

@@ -143,7 +143,7 @@ jobs:
           RUSTFLAGS: "-Cinstrument-coverage"
           LLVM_PROFILE_FILE: "retworkx-%p-%m.profraw"
       - name: Run tests
-        run: cd tests && python -m unittest discover . && cd ..
+        run: cd tests && stestr run && cd ..
         env:
           LLVM_PROFILE_FILE: "retworkx-%p-%m.profraw"
       - name: Run grcov

noxfile.py

@@ -33,7 +33,7 @@ def install_rustworkx(session):
 def base_test(session):
     install_rustworkx(session)
     session.chdir("tests")
-    session.run("python", "-m", "unittest", "discover", *session.posargs)
+    session.run("stestr", "run", *session.posargs)
 
 @nox.session(python=["3"])
 def test(session):

tox.ini

@@ -27,7 +27,7 @@ passenv =
   RUSTWORKX_DEBUG
 changedir = {toxinidir}/tests
 commands =
-  python -m unittest discover {posargs}
+  stestr run {posargs}
   python -c "print('\nrustworkx no longer supports tox. Please run the equivalent comand with nox:\n\n\tnox -e test\n')"
 
 [testenv:lint]