Support opt-out of extra derived traits for rejections for #[derive(FromRequest)] (#729)

* Handle structs without fields

* Support opt-out of derived rejection traits

* Handle duplicate opt outs

* Improve error if opting out of `Display` or `Debug` but not `Error`

* document `rejection_derive`

* Handle using both `via` and `rejection_derive`

* don't derive debug for `RejectionDeriveOptOuts`

* Update axum-macros/src/from_request.rs

Co-authored-by: Jonas Platte <[email protected]>

Co-authored-by: Jonas Platte <[email protected]>

axum-macros/tests/from_request/pass/empty_tuple.rs

@@ -0,0 +1,12 @@
+use axum_macros::FromRequest;
+
+#[derive(FromRequest)]
+struct Extractor();
+
+fn assert_from_request()
+where
+    Extractor: axum::extract::FromRequest<axum::body::Body, Rejection = std::convert::Infallible>,
+{
+}
+
+fn main() {}