Import diffusion training schemas from models.training directly

The import-hoist lint flags newly re-exported names in the models/__init__.py hub as
unused (it does not treat __all__ membership as a use). Import the three diffusion
training schemas straight from models.training in routes/training.py, where they are
used in the route annotations and calls, and drop the __init__ re-export.

studio/backend/models/__init__.py

@@ -14,9 +14,6 @@ from .training import (
     TrainingRunDetailResponse,
     TrainingRunDeleteResponse,
     TrainingRunUpdateRequest,
-    DiffusionTrainingStartRequest,
-    DiffusionTrainingStartResponse,
-    DiffusionTrainingStatusResponse,
 )
 from .models import (
     CheckpointInfo,
@@ -75,9 +72,6 @@ from .data_recipe import (
 __all__ = [
     # Training schemas
     "TrainingStartRequest",
-    "DiffusionTrainingStartRequest",
-    "DiffusionTrainingStartResponse",
-    "DiffusionTrainingStatusResponse",
     "TrainingJobResponse",
     "TrainingStatus",
     "TrainingProgress",

studio/backend/routes/training.py

@@ -56,6 +56,8 @@ from models import (
     TrainingJobResponse,
     TrainingStatus,
     TrainingProgress,
+)
+from models.training import (
     DiffusionTrainingStartRequest,
     DiffusionTrainingStartResponse,
     DiffusionTrainingStatusResponse,