shed: include invariant checks as part of migration testing

[arajasek]

Related Issues

Towards #9246

Proposed Changes

You can now run, eg., lotus-shed migrate-nv17 --check-invariants bafy2bzacedbxlti4ol2ipyd7nqhl5x6242xl4lt6twibwtnqmyt3ivfbub3y6, which will invoke the full suite of invariant checks (see here).

Note that the checks will likely take 2-3 hours to complete, and there are currently some minor invariant failures in the power actor (inherited from v8).

Additional Info

Checklist

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