refactor(gateway): 重构格式转换候选资格检查并优化测试基础设施

- 将 format_conversion_disabled 的过滤提前到候选遴选阶段，替代原来的 skip_reason 标记机制
- 为测试添加 execution_runtime_sync_override 直接注入支持，避免启动额外 HTTP 服务器
- 将 submit_terminal_event 改为 async record_terminal_event 确保失败用量事件可靠入库
- 新增 test_support 模块封装可重试的 loopback 端口绑定逻辑
- 前端：poolTrace 将 skipped 从隐藏状态移除，新增 buildPoolParticipatedCandidates 统一新旧链路逻辑，并将 skipped 状态色改为 foreground

apps/aether-gateway/src/tests/usage.rs

@@ -27,9 +27,9 @@ use serde_json::json;
 use sha2::{Digest, Sha256};
 
 use super::{
-    any, build_router_with_state, build_state_with_execution_runtime_override, start_server, Body,
-    HeaderValue, Json, Mutex, Request, Response, Router, StatusCode, UsageRuntimeConfig,
-    TRACE_ID_HEADER,
+    any, build_router_with_state, build_state_with_execution_runtime_override, send_request,
+    start_server, Body, HeaderValue, Json, Mutex, Request, Response, Router, StatusCode,
+    UsageRuntimeConfig, TRACE_ID_HEADER,
 };
 use crate::data::GatewayDataState;