fix: handle ConflictError in JobHandler and add corresponding tests

[razbroc]

This pull request introduces improved handling of conflict scenarios in job and task management, specifically ensuring that tasks are not erroneously rejected or notified when a conflict (such as an already aborted job) occurs. It also adds comprehensive unit tests to verify this behavior.

Error Handling Improvements:

• Updated JobHandler (src/job/models/jobHandler.ts) to detect ConflictError instances and, in such cases, log a warning and skip both task rejection and job notification, allowing the polling loop to continue without side effects. [1] [2]

Testing Enhancements:

• Added a unit test in jobHandler.spec.ts to assert that ConflictError does not trigger task rejection or job notification, ensuring correct error handling. [1] [2]
• Added a unit test in tileMergeTaskManager.spec.ts to verify that a ConflictError during batch publishing (HTTP 409) causes the process to stop immediately and does not continue enqueuing tasks. [1] [2]

Question	Answer
Bug fix	✔
New feature	✖
Breaking change	✖
Deprecations	✖
Documentation	✖
Tests added	✔
Chore	✔

Related issues: #XXX , #XXX ...
Closes #XXX ...