Macro repository_impl

macro_rules! repository_impl {
    ($repo_trait:ident:
        $(
            async fn $method:ident (
                &mut self
                $(, $arg:ident: $arg_ty:ty )*
                $(,)?
            ) -> Result<$ret_ty:ty, Self::Error>;
        )*
    ) => { ... };
}

A macro to implement a repository trait for the MapErr wrapper and for Box<R>