Macro impl_option_try_from_sexp 

macro_rules! impl_option_try_from_sexp {
    ($t:ty) => { ... };
}

Implement TryFromSexp for Option<T> where T already implements TryFromSexp.

NULL → None, otherwise delegates to T::try_from_sexp and wraps in Some.

Crate-internal: the orphan rule forbids impl TryFromSexp for Option<T> outside miniextendr-api (#1731), so this only expands here.