Should we integrate with `annotated-types`?

Follow up from #176 and #154.

We currently support adding constraints to types by annotating them with msgspec.Meta. annotated-types provides it's own annotations describing the same constraints - we could potentially integrate with them in 2 ways:

• Consume annotated-types annotations. This would let msgspec work with annotated types annotations as well as our own built-in Meta annotations.
• Produce annotated-types annotations. This would make Meta.__iter__ produce the equivalent annotated-types annotations, letting it work with other tools that consume such types.

I'm not convinced there's a real use case for either of these integrations, and would want to hear from multiple real users before expending any effort supporting this. See https://github.com/jcrist/msgspec/pull/176#issuecomment-1229265714 for a longer write up of my thoughts.

Start by reading follow-ups #176 and #154, then review the linked pull request discussion and the behavior of Meta.iter. Compare the two proposed integration directions—consuming or producing annotated-types annotations—and look for concrete user needs. The issue is done only once a supported direction and scope have been agreed.