test: Add invariance checks to v17 migration test

[geoff-vball]

Related Issues

Implements part of #9246

Proposed Changes

Tests the following invariants for the v17 migration:

• that for each pending, verified deal in v8 market, there is a corresponding allocation in v9 verifreg Allocations
• that nextAllocationID is equal to the number of pending, verified deals in v8 market
• that for each pending, verified deal in v8 market, there is a corresponding entry in v9 market PendingDealAllocationIds
• that all miners that have PreCommits with deals in them have non-nil UnsealedCid, and this CID is correctly calculated:

Additional Info

Checklist

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• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
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• This PR has tests for new functionality or change in behaviour
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