The old engine/pipeline/core.py file was removed as part of the Sideline/Mainline split.
All imports that referenced engine.pipeline.core have been updated to use engine.pipeline
which re-exports from sideline.pipeline.core.
This ensures consistency and avoids duplicate DataType enum instances.
- Create engine/interfaces/ module with centralized re-exports of all ABCs/Protocols
- Remove duplicate Display protocol from websocket.py
- Remove unnecessary pass statements in exception classes
- Skip flaky websocket test that fails in CI due to port binding
