feat: state: skip tipset execution when possible

[Stebalien]

Proposed Changes

Instead of always executing the tipset inside StateManager.TipSetState, try to find a successor tipset and return the parent state & receipts as recorded.

Checklist

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[arajasek]

Wow, I like how simple this is!

[raulk]

Merged so I can build on it. Thanks, @Stebalien!

[raulk]

Note: I think @arajasek had expressed a pet peeve against using "deeper" methods from the Eth API (e.g. a StateManager method in this case).