[NV13/Simulation] Feature to export state

[Stebalien]

Simulation branch: #6406

We need a way to easily export state to a CAR from a simulation. I've written a command to export an arbitrary DAG, but it would be nice to have something a little more integrated to export a specific actor's state at a specific epoch on a specific simulation. E.g.:

lotus-sim [--simulation=...] state [--height=...] export [f0....]

Where the height, simulation, and actor are optional (if no actor is specified, we should export the state-tree.

[magik6k]

We could integrate this with the chain get /ipld/path/with/the/selector/like/thing/@Ha:t0123/@state command (and add an --export flag to it)

(for that to work we also would need to update the lotus resolveOnce to work with different h/amt versions / widths (possibly just using ctx values to carry some metadata about network version))

[Stebalien]

Yeah. The main issue is that the lotus simulation runs offline and I'd rather not spin up a node just to export something. Ideally the simulation would run as a daemon and expose the API, but that's more complicated.

But we may be able to re-use some of the logic?

[magik6k]

It should be easy to just export the resolveOnce func, and use it in the export command in lotus-shed (#6405)