/// Converts a borrowed memoized `Option` or `Result` into the ergonomic
/// borrowed shape exposed by `#[memoize]`.
///
/// `#[memoize]` stores the function's original return value in the request
/// cache and normally returns `&T`. For top-level `Option<T>` and
/// `Result<T, E>` return values, the macro applies `.as_ref()` and publishes
/// this associated type instead, yielding `Option<&T>` and `Result<&T, &E>`.