refactor: use better algo for determining highest

src/inventory_wars/scoring.py

@@ -34,16 +34,16 @@ class FirstGuess(Scoring):
 
 class HighestAmount(Scoring):
     def __init__(self):
-        self.shares: set[ItemShare] = set()
+        self.max: ItemShare | None = None
 
     def calculate_score(self, item: ItemShare) -> int:
-        self.shares.add(item)
+        if self.max is None or item.count > self.max.count:
+            self.max = item
         return 0
 
     def calculate_end_score(self) -> ItemShare | None:
-        highest = max(self.shares, key=lambda s: s.count)
-        highest.score = 1
-        return highest
+        self.max.score = 1
+        return self.max
 
 
 class FirstThenHighest(Scoring):