[Feature Request]: 获取用户收藏相关API添加返回 `nsfw` 字段

**你想添加的新功能**

希望下面两个API新增支持返回 `nsfw` 字段

`/v0/users/{username}/collections`
`/v0/users/{username}/collections/{subject_id}`

**你希望的解决方案**

**其他可能的替代方案**

**其他相关信息**

Locate the handlers and response models for `/v0/users/{username}/collections` and `/v0/users/{username}/collections/{subject_id}`. Read any nearby tests or API definitions first, then verify that both collection responses include the `nsfw` field and that the relevant tests pass.

Written by the indexing model from the issue text.