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'

86_Target/python/target.py

@@ -55,7 +55,7 @@ def prompt():
 
 
 def next_target():
-    for i in range(5):
+    for _ in range(5):
         print()
     print("NEXT TARGET...")
     print()