Dataset in TMD 8.x not anymore savable by nippy

[behrica]

So I cannot "freeze" anymore data structures which have a "dataset" somewhere in the middle.
(I am aware that requiring 'tech.v3.dataset.io.nippy') fixes this,
but this is not obvious

[harold]

Thank you!

Context: https://clojurians.zulipchat.com/#narrow/channel/236259-tech.2Eml.2Edataset.2Edev/topic/TDM.208.2E012.20and.20nippy