fix: Update imports to use engine.pipeline instead of engine.pipeline.core

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.

engine/interfaces/__init__.py

@@ -28,7 +28,7 @@ from engine.effects.types import (
     apply_param_bindings,
     create_effect_context,
 )
-from engine.pipeline.core import (
+from engine.pipeline import (
     DataType,
     Stage,
     StageConfig,