Consider using Rc<str> and other copy-friendly types when returning DNS data to the user.

This library is really cool, thanks for making this.

When rendering the results in my app, I found that I `clone()` `String` a lot. Since the results returned are not meant to be mutated by the user, it would be nice if those copies were just an increment of the reference count and not actual data copies.

I am not sure how to best approach this, however, because some users may wish to use an `Arc` instead. My current usecase is making `dig` in the browser with WASM and I do not need to use `Arc`s just yet. But may a type alias and a feature flag to turn that type alias into an `Arc` is the way to go.