Update to more pythonic template

Author: jwl-7

src/code/python/dynamic_programming/top_down.py

@@ -1,16 +1,8 @@
 def fn(arr):
+    @cache
     def dp(STATE):
         if BASE_CASE:
             return 0
-
-        if STATE in memo:
-            return memo[STATE]
-
-        ans = RECURRENCE_RELATION(STATE)
-        memo[STATE] = ans
-
-        return ans
-
-    memo = {}
+        return RECURRENCE_RELATION(STATE)
 
     return dp(STATE_FOR_WHOLE_INPUT)