CAR-1283: align cache.py to dev (bytes-aware decode, drop str() cast)

src/cartsnitch_api/cache.py

@@ -35,10 +35,12 @@ class CacheClient:
     async def get(self, key: str) -> str | None:
         if not self._client:
             return None
-        result = await self._client.get(key)
+        value = await self._client.get(key)
-        if result is None:
+        if value is None:
             return None
-        return str(result)
+        if isinstance(value, bytes):
+            return value.decode("utf-8", errors="replace")
+        return value
 
     async def set(self, key: str, value: str, ttl_seconds: int = 300) -> None:
         if not self._client: