Add additional tests for lib-sourcify

[manuelwedler]

follow-up of #1429

I found parts of lib-sourcify for which it would be nice to add additional tests. We generally want to increase our test coverage. The following parts need additional tests:

• The hashFunctions folder has only about 50 % coverage. We should write tests that hash some file with ipfsHash and swarmHash. It should be easy to get a high coverage above 90 % here.
• SourcifyChain: There is some code regarding contracts created by factories that is uncovered. I specifically mean lines 388 - 417 and 194 - 234. These should be tested.
• validation.ts and verification.ts: These are quite critical components and they have some functions and rather important branches uncovered. I won't go into details here. I think it would be sufficient to get them at least to 90 % coverage.