Implement unit tests for the AllianceDatabaseService

[manuelwedler]

Writing to the VerA db was broken after one release, because we use a different constraint in contract_deployments on Sourcify matches now. If we would had tests for the AllianceDatabaseService we would have caught this problem before the release. Therefore, we should implement tests for all functions of the AllianceDatabaseService.

I would implement these as unit tests and not run the verification through the server API. Just calling the functions on a AllianceDatabaseService instance should be good for catching the errors we had.

Maybe we can generalize these unit tests, such that we can also run it with the SourcifyDatabaseService.

Related

Fix for the constraint to work with both dbs: #2020