Macro into_r_infallible 

macro_rules! into_r_infallible {
    ($ty:ty, |$recv:ident| $body:expr) => { ... };
}

Generate an infallible IntoR impl whose only real method is into_sexp.

Collapses the four-line boilerplate shell shared by every Infallible IntoR impl in the optional-type modules: try_into_sexp delegates to into_sexp, try_into_sexp_unchecked delegates to try_into_sexp, and into_sexp_unchecked is left as the trait default. Only the into_sexp body is supplied, as a closure-style |recv| expr binding the receiver (a macro cannot reuse a self that arrives through a fragment, so the caller names it). The generated methods are byte-identical to the hand-written shell, so this is purely a dedup.

into_r_infallible!(Uuid, |this| this.to_string().into_sexp());
into_r_infallible!(Vec<Uuid>,
    |this| this.into_iter().map(|u| u.to_string()).collect::<Vec<_>>().into_sexp());