fix: unify default latency test URL and update workflows/backend logic

- All delay test logic, Rust MihomoManager, API, cmds, delay.ts, settings, and group editor now use the Cloudflare 204 test URL
- Fixed outdated URLs in docs and comments
- Fix Github Actions workflow: unexpected neeeds run

src/services/delay.ts

@@ -23,7 +23,7 @@ class DelayManager {
       `[DelayManager] 获取测试URL，组: ${group}, URL: ${url || "未设置"}`,
     );
     // 如果未设置URL，返回默认URL
-    return url || "https://www.gstatic.com/generate_204";
+    return url || "https://cp.cloudflare.com/generate_204";
   }
 
   setListener(name: string, group: string, listener: (time: number) => void) {