Set versioning pattern to earlySemver versioning in sbt

[Baccata]

to help downstream users ... but also after we assess how much of a pain it'll be to try to guarantee backward compat

[keynmol]

I think this would be a good opportunity to lock down some of the internal-ish traits that we have exposed.

The only argument against that I can see is keeping integration points open (*Aux classes and unsealed TestOutcome), the rest of the hierarchy can be probably locked down.