Add Cookie extractor for typed cookie access

[arferreira]

Summary

• Add Cookie<T> extractor for deserializing cookies into typed structs
• Parse Cookie header and deserialize to target type via serde
• Returns 400 Bad Request if required cookies are missing

Usage

#[derive(Deserialize)]
struct Session {
    session_id: String,
}

#[get("/dashboard")]
async fn dashboard(session: Cookie<Session>) -> Result<Json<Dashboard>> {
    let data = session.into_inner();
    // ...
}

Related Issues

Closes #85

Checklist

• cargo fmt passes
• cargo clippy has no warnings
• Tests pass
• Documentation updated (if needed)

[juv]

Serializing to JSON and then deserializing from JSON to T looks interesting. Is this a good approach (genuinely asking)?

[arferreira]

fair point! it's a pragmatic shortcut, cookies are always k/v pairs, so the json roundtrip works, but yeah it's not the ideal world, I think maybe a direct Hashmap<String, String> -> T would be cleaner, good candidate for a follow-up improvement.

[juv]

Missing changes to docs: https://github.com/arferreira/rapina/blob/main/docs/content/guide/extractors.md