chore: fix mypy violations in post_training modules

Note: this patch touches all files but post_training.py that will be
significantly changed by #1437, hence leaving it out of the picture for
now.

running_loss is now always Tensor (on-device) and doesn't change its
type from int to Tensor (which made mypy unhappy).

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

docs/_static/llama-stack-spec.yaml

@@ -6615,15 +6615,6 @@ components:
       required:
         - results
       title: ScoreBatchResponse
-    AlgorithmConfig:
-      oneOf:
-        - $ref: '#/components/schemas/LoraFinetuningConfig'
-        - $ref: '#/components/schemas/QATFinetuningConfig'
-      discriminator:
-        propertyName: type
-        mapping:
-          LoRA: '#/components/schemas/LoraFinetuningConfig'
-          QAT: '#/components/schemas/QATFinetuningConfig'
     LoraFinetuningConfig:
       type: object
       properties:
@@ -6707,7 +6698,9 @@ components:
         checkpoint_dir:
           type: string
         algorithm_config:
-          $ref: '#/components/schemas/AlgorithmConfig'
+          oneOf:
+            - $ref: '#/components/schemas/LoraFinetuningConfig'
+            - $ref: '#/components/schemas/QATFinetuningConfig'
       additionalProperties: false
       required:
         - job_uuid