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'

65_Nim/python/Traditional_NIM.py

@@ -68,7 +68,7 @@ class NIM:
 
     def check_for_win(self):
         sum = 0
-        for k, v in self.piles.items():
+        for v in self.piles.values():
             sum += v
 
         if sum == 0: