test(scan): Add raw database format snapshots to the scanner

[teor2345]

Motivation

These are part of the standard database tests in #8069.

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Complex Code or Requirements

Not really, it's just the same as the state.

Solution

• Add snapshot tests for the raw scanner database format
• Expose database test support code in zebra-state
• Expose test support code in zebra-scan

Related changes:

• Make scanner storage methods clearer and easier to use
• Move scanner tests to a submodule

Testing

These are extra tests.

I have manually checked the data formats in the snapshots and they appear correct.

Review

Because of the code movement, the state db test APIs, and the storage API changes, this PR blocks other tests. So it would be good to get it merged soon. It doesn't need to be in the release.

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• Does the PR scope match the ticket?
• Are there enough tests to make sure it works? Do the tests cover the PR motivation?
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Follow Up Work

The rest of the tests in #8069

[oxarbitrage]

codespell failed, restarting: https://github.com/ZcashFoundation/zebra/actions/runs/7141093973/job/19447724265?pr=8075

[teor2345]

Thanks for fixing up the imports, that was a bit of a mistake from me!

[oxarbitrage]

looks good to me.

[arya2]

Looks good!