fix: LookupVerifier returns interface (#2631)

[ibukanov]

Fix the signature of the LookupVerifier method of the Keystore interface to return Verifier interface directly, not a pointer to it to simplify implementations of the method.

Summary

Type of Change

• Product feature
• Bug fix
• Performance improvement
• Refactor
• Other

Tested Environments

• Development
• Staging
• Production

Before Requesting Review

• Does your code build cleanly without any errors or warnings?
• Have you used auto closing keywords?
• Have you added tests for new functionality?
• Have validated query efficiency for new database queries?
• Have documented new functionality in README or in comments?
• Have you squashed all intermediate commits?
• Is there a clear title that explains what the PR does?
• Have you used intuitive function, variable and other naming?
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• Have you performed a self review of this PR?

Manual Test Plan

[pavelbrm]

Also tagged @clD11 for the Wallet service.

[pavelbrm]

I don't see a reason it was needed to be done that way. Pointers to interfaces are sometimes needed and useful (like keeping a set of them), but in this particular case it seem more like a mistake.

Approving. It would be nice to get one from @clD11 as well.