Bring the scala3-v2 branch up-to-date, review, publish

[adamw]

We've started work on Magnolia v2 for Scala 3 some time ago, which included support for AnyVals some time ago, but the effort has stalled. Since then, the scala3 and scala3-v2 branches have diverged. This is a an umbrella task to fix this situation and push the v2 release:

• [ ] merge any changes from scala3 to scala3-v2
• [ ] review & merge https://github.com/softwaremill/magnolia/pull/457#issuecomment-2439985577
• [ ] verify that https://github.com/softwaremill/magnolia/issues/550#issuecomment-2435575118 is fixed with the new release, update magnolia usages in tapir
• [ ] make sure all scala 3 & scala 2 types are supported in the new release
• [ ] review the code to make sure the API & macro usage is consistent