Investigate multi-agent integration tests using the new test framework

[VictorCavichioli]

Story Description:
Currently, ecChronos lacks integration tests that validate behavior in multi-agent environments, which led to undetected issues such as incorrect job execution across agents. The standalone-integration tests cover single-agent scenarios but do not replicate a distributed, multi-agent environment. The proposed improvement is to leverage the new test framework to enable the execution of the same suite of tests currently used in standalone-integration, but in a multi-agent setup simulating a Cassandra cluster managed by multiple ecChronos agents. This will help identify and prevent future synchronization and job allocation issues between agents.

Acceptance Criteria:

1. The new test framework can spin up multiple ecChronos agents connected to a distributed Cassandra cluster.
2. All current standalone-integration test cases can be executed in the multi-agent environment without modification to their core logic.
3. Additional tests are added to cover scenarios unique to multi-agent setups, such as multi-agent repair coordination and job ownership verification.
4. Test runs provide clear logging that distinguishes actions taken by different agents.

Definition of Done:

1. Multi-agent test execution fully automated within the CI pipeline.
2. Documentation updated to explain how to run multi-agent tests locally and in CI.
3. Tests pass consistently and cover known multi-agent bug cases (including the on-demand repair job ownership issue)

Notes:
Related with #652