Clean Code: Python

Fix issues found by flake8-bugbear:

* Unused loop variables
* assert statements in non-test code
* mixing test code with production code
* mark one excessive test which takes ~10min to run
  as 'slow'

00_Utilities/python/ci-requirements.in

@@ -1,3 +1,4 @@
 pytest
 flake8
+flake8-bugbear
 mypy

00_Utilities/python/ci-requirements.txt

@@ -5,8 +5,14 @@
 #    pip-compile ci-requirements.in
 #
 attrs==21.4.0
-    # via pytest
+    # via
+    #   flake8-bugbear
+    #   pytest
 flake8==4.0.1
+    # via
+    #   -r ci-requirements.in
+    #   flake8-bugbear
+flake8-bugbear==22.1.11
     # via -r ci-requirements.in
 iniconfig==1.1.1
     # via pytest