Probably don't merge - Upickle 3 note

[Quafadas]

I lost quite a bit of time, figuring out that a transitive change to upickle 3 required explicit derivation of case objects.

This is a vey quick docs PR in case the knowledge saves time.

[Quafadas]

As an aside, moving to upickle 3+ made a big difference in compile times in my scala 3 project