feat(codex): prefer upstream websockets for responses

[hemo94931]

配置项中添加：codex-prefer-upstream-websockets: false
用于控制 codex下游http/sse连接cpa时，cpa是否使用websocket与OpenAI建立连接（需要auth的json文件配置"websockets":true，否则回退为http）

[gemini-code-assist]

Code Review

This pull request introduces the codex-prefer-upstream-websockets configuration option, allowing ordinary HTTP/SSE requests to prefer Codex credentials configured with websockets and utilize the upstream websocket transport. It adds context helpers to propagate this preference, updates the CodexAutoExecutor to route requests accordingly, and modifies the scheduler and selector logic to prioritize websocket-enabled credentials when the preference is active. Additionally, comprehensive unit tests have been added to verify the new behavior. I have no feedback to provide as there are no review comments to address.