Add beatmapsets Download load balancing

app/dependencies/beatmap_download.py

@@ -0,0 +1,8 @@
+from __future__ import annotations
+
+from app.service.beatmap_download_service import download_service
+
+
+def get_beatmap_download_service():
+    """获取谱面下载服务实例"""
+    return download_service