[v1] Refactor kernel plugin (#9669)

Co-authored-by: frozenleaves <frozen@Mac.local>

src/llamafactory/hparams/model_args.py

@@ -173,7 +173,7 @@ class BaseModelArguments:
         default=True,
         metadata={"help": "Whether or not to use KV cache in generation."},
     )
-    use_v1_kernels: bool = field(
+    use_v1_kernels: bool | None = field(
         default=False,
         metadata={"help": "Whether or not to use high-performance kernels in training."},
     )