Add `time` to `Basin / state`

[visr]

Basin / state currently only has node_id and level. I think we should add the single timestamp that the state represents as well to the results.

Since we want to be able to use state results directly as inputs, that means it should also support time as an input.

We could go the strict route and require that the input state time matches the simulation start time. Though in my experience this tends to be annoying, because you may want to use a warm state from another timestamp to get the model up to speed faster. We could do this:

• always write state time to results
• if input state has no time or matching starttime, run normally like now
• if input state has different time than starttime, log a warning