Allow storage of name-based UUIDs

We can handle UUIDs of any type if we stop asserting the type to be 1 or 4.

[`uuid_variant`](https://github.com/karelzak/util-linux/blob/v2.24.1/libuuid/src/uuid_time.c#L86) always returns a value between `UUID_VARIANT_NCS` and `UUID_VARIANT_OTHER`, so we can stop checking that every time.