feat(scanner): Restart scanning where left

[oxarbitrage]

Motivation

We want the scanner to have the ability of resume the scanning where it was left after a restart.

Close #8022

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Solution

I am pushing for a solution that involves adding a control empty result entry to the database for each key every X blocks. This is because a very probable scenario is that the key do not have any real transaction close to sapling (all new accounts).

Testing

The functionality is tested by adding an acceptance test that needs a cache state close to tip.

Review

@teor2345 had been working with me in this.

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Follow Up Work

This PR does not include the cases of new keys/deleted keys in the config that are part of #8022

It will be done in a separated PR.

[oxarbitrage]

A few comments and doubts i have.

[teor2345]

Most of this looks good, but I think we need to count our keys and heights carefully. This might need some unit tests to be sure.

Let's do a video review and talk through the database reading loop?

[teor2345]

I left some TODOs in PR #8075 and #8083 about testing this code using snapshots. So let's open another ticket to do that once they all merge?

I think that would cover most of the testing for this PR, except maybe for some unit tests for skipped keys and skipped heights.

[teor2345]

Looking good now, let me know if you want help with the height we start fetching blocks.

[teor2345]

Thanks for working through this, let's see how it goes!