Reduce usage of async_trait

[Nutomic]

There is a lot of unnecessary usage of async_trait which can be replaced with standard Rust functionality. This is preferable as less macro usage means faster compilation, and it uses static dispatch (meaning it chooses at compile time which code to execute, unlike async_trait macro which decides at runtime). However the trait definition is a little more verbose as it cannot use async fn but use fn with -> impl Future.

[dessalines]

I still see a good amount of these in crates/apub/, and you might as well remove the top level workspace dep in Cargo.toml

[Nutomic]

Moved the dependency. The remaining usage of async_trait cannot be removed because it uses dynamic dispatch, which is not supported by the standard library yet.