fix(discord-cross): 修复跨平台消息处理和附件下载问题

修复QQ群消息处理中的非群消息过滤问题
优化Discord附件下载逻辑，使用aiohttp替代requests
修复Redis订阅任务重复创建问题
调整消息格式化的embed字段处理逻辑

plugins/discord-cross/parser.py

@@ -327,13 +327,14 @@ async def format_qq_to_discord_content(
             "name": f"{qq_nickname}",
             "icon_url": f"https://q1.qlogo.cn/g?b=qq&nk={qq_user_id}&s=640"
         },
-        "description": content if content else "",
-        "timestamp": None,
         "footer": {
             "text": f"来自 QQ"
         }
     }
     
+    if content:
+        embed["description"] = content
+    
     if attachments:
         image_urls = []
         voice_urls = []
@@ -364,7 +365,10 @@ async def format_qq_to_discord_content(
                 filtered_attachments.append(att)
         
         attachments = filtered_attachments
-        embed["description"] = content if content else ""
+        if content:
+            embed["description"] = content
+        elif "description" not in embed:
+            embed["description"] = ""
         
         if image_urls:
             embed["image"] = {"url": image_urls[0]}