upgrade.MIGRATIONS

Every migration, oldest first. One step covers every alpha and beta

upgrade.MIGRATIONS: list[Migration] = [
    Migration(
        version=CONFIG_VERSION,
        title="Bring an older dataset to the current format",
        plan=_plan_all,
        apply=_apply_all,
    )
]

format; when the format changes again, add a part to _PARTS (and bump CONFIG_VERSION).