Against SemVer

- Finger to the wind ("this feels like a big change"). - Domain-specific versioning scheme (so Ruff uses [this variant](https://docs.astral.sh/ruff/versioning/#version-changes) that seems reasonable to me; it's described as a SemVer variant, but the work to specify how various cases are handled seems very useful to me). - As you say, time stamps. FWIW I don't like that very much, because time is often so weakly correlated with progress / "breakingness," but it has its proponents.