Add Claim Publisher integration tests

[GMKrieger]

📚 Context

The component's main logic was previously validated using a mocked version of the repository at #479. With the database functionality implemented after #480, we should write more tests in an environment closer to the real one to increase our confidence in the code.

✔️ Solution

Add integration tests between the Claim Publisher and the repository, using the testcontainers library to create a test database in a Docker container.

📈 Subtasks

• Test it finishes an empty epoch
• Test it finishes an epoch with outputs