[Bugfix] Fix type annotations in CPU model runner (#4256)

Author: WoosukKwon

vllm/worker/cpu_model_runner.py

@@ -73,7 +73,8 @@ def load_model(self) -> None:
     def _prepare_prompt(
         self,
         seq_group_metadata_list: List[SequenceGroupMetadata],
-    ) -> Tuple[torch.Tensor, torch.Tensor, AttentionMetadata, List[int]]:
+    ) -> Tuple[torch.Tensor, torch.Tensor, AttentionMetadata, List[int],
+               Optional[torch.Tensor]]:
         assert len(seq_group_metadata_list) > 0
         input_tokens: List[int] = []
         input_positions: List[int] = []
@@ -347,8 +348,8 @@ def _prepare_sample(
     def prepare_input_tensors(
         self,
         seq_group_metadata_list: List[SequenceGroupMetadata],
-    ) -> Tuple[torch.Tensor, torch.Tensor, AttentionMetadata,
-               SamplingMetadata]:
+    ) -> Tuple[torch.Tensor, torch.Tensor, AttentionMetadata, SamplingMetadata,
+               Optional[torch.Tensor]]:
         multi_modal_input = None
         if self.is_driver_worker:
             # NOTE: We assume that all sequences in the group are all prompts or