Godbolt example

The following functions when used on optional<T&> of && fail to compile:

value();
operator*();
and_then();
transform();

• For value() and operator*() it appears that the && and const && return the wrong type.
• and_then() and transform() issues seem related to the above
• It appears there is missing test coverage for this too.
• Also operator-> is wrong.

Obviously, since I'm the one that provided this implementation (apologies!), I'll work on fixing it.