Revise test suite's ordering.

- First run unit tests (which are the more problematic).
- Then run code quality verifications (pylint / mypy / black).
- Finally run integration tests.

The rationale to inverting the last two items relative to what was
done prior to this update is to keep the longest-running tests for
the end (rather than re-play a long pipeline due to late-detected
formatting issues).

tox.ini

@@ -15,12 +15,6 @@ commands=
         --cov --cov-report= \  # reset then accumulate coverage quietly
         --ignore=test/functional/ \
         test
-    # run functional tests (that build on units)
-    pytest {posargs} \
-        --cov --cov-append --cov-report=term \  # acc. and display coverage
-        test/functional/
-    # export the finalized coverage report to xml
-    coverage xml
     # verify code acceptance by pylint
     pylint declearn
     pylint --recursive=y test
@@ -29,6 +23,12 @@ commands=
     # verify code formatting
     black --check declearn
     black --check test
+    # run functional ~ integration tests (that build on unit ones)
+    pytest {posargs} \
+        --cov --cov-append --cov-report=term \  # acc. and display coverage
+        test/functional/
+    # export the finalized coverage report to xml
+    coverage xml
 
 [pytest]
 addopts = --full-trace