general: move reddit tests into my/tests + tweak my.core.cfg to be more reliable

tox.ini

@@ -79,6 +79,13 @@ commands =
 
     hpi module install my.reddit.rexport
 
+    {envpython} -m pytest \
+        # importlib is the new suggested import-mode
+        # without it test package names end up as core.tests.* instead of my.core.tests.*
+        --import-mode=importlib     \
+        --pyargs my.tests \
+        {posargs}
+
     {envpython} -m pytest tests \
             # ignore some tests which might take a while to run on ci..
             --ignore tests/takeout.py        \