[Feature] 中转站偶发 HTTP 520 / 521 / 525 不会自动重试

[ViCrack]

Affected area

Model providers

Problem statement (what should this solve)

用中转站时，上游偶尔返回 HTTP 525（Cloudflare SSL Handshake Failed）/ 520，请求直接失败。

Proposed behavior

让 525 520 521 等 走现有重试 + 指数退避。

就像524一样

也可考虑支持手动重试恢复的功能（这样就不需要手动打继续了）

Estimated change scope

Alternatives considered

https://developers.cloudflare.com/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-520/

把cloudflare常见报错都纳入自动重试

Pre-submit checklist

• I searched existing issues and pull requests and found no duplicates.
• This proposal is focused on a single feature or improvement.
• I understand a PR should come after this issue is confirmed by maintainers, otherwise it will be converted to draft.