Currently, the integration tests setup is copy-pasted between each test. In this diff, TestRunner is added so we can abstract this setup away so tests can focus on the actual test.
Previous attempts tried to add a `ecash-test-utils` package with this class, however, since it depended on both chronik-client and ecash-lib (which in turn depended on `ecash-test-utils`), it was very difficult to resolve this circular dependency, so this approach has been dropped.