fix: use expires_at directly for DynamoDB TTL timestamp

The managed_entry.ttl property returns remaining seconds from NOW, not the
original TTL duration. This caused incorrect TTL timestamps when there was
any delay between entry creation and property access. Using expires_at
directly ensures the timestamp is always correct.

Fixes test failures in older dependency versions where timing delays
were more common.

Co-authored-by: William Easton <strawgate@users.noreply.github.com>

Author: github-actions[bot]

key-value/key-value-aio/src/key_value/aio/stores/dynamodb/store.py

@@ -226,9 +226,9 @@ async def _put_managed_entry(
         }
 
         # Add TTL if present
-        if managed_entry.ttl is not None and managed_entry.created_at is not None:
+        if managed_entry.expires_at is not None:
             # DynamoDB TTL expects a Unix timestamp
-            ttl_timestamp = int(managed_entry.created_at.timestamp() + managed_entry.ttl)
+            ttl_timestamp = int(managed_entry.expires_at.timestamp())
             item["ttl"] = {"N": str(ttl_timestamp)}
 
         await self._connected_client.put_item(  # pyright: ignore[reportUnknownMemberType]