style: ruff format 全仓库

行宽 180 下把历史遗留的折行表达式合并，无语义改动。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

contest/models.py

@@ -75,7 +75,6 @@ class ACMContestRank(AbstractContestRank):
         ]
 
 
-
 class ContestAnnouncement(models.Model):
     contest = models.ForeignKey(Contest, on_delete=models.CASCADE)
     title = models.TextField()