Rollup merge of rust-lang#103432 - jsha:box-is-not-notable, r=GuillaumeGomez

rustdoc: don't mark Box<T> as Iterator, Read, etc

Because Box<T> has pass-through implementations, rustdoc was giving it the "Notable Traits" treatment for Iterator, Read, Write, and Future, even when the type of T was unspecified.

Pin had the same problem, but just for Future.

Fixes rust-lang#100320

Author: Yuki Okushi