fix: eth: plug sqlite leak

[geoff-vball]

Related Issues

Alternative implementation of #10143

Proposed Changes

Calling db.Query() gives back a file-descriptor that has to be closed and was causing fd leaks. Since we're querying unique values, we can just call db.QueryRow() which is more succinct and doesn't cause leaks.

Additional Info

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[raulk]

I think we had identified this in the original review -- glad we're fixing it!