refact attn metadata build

Signed-off-by: weiguihua2 <[email protected]>

Author: weiguihua2

vllm_ascend/attention/utils.py

@@ -36,7 +36,7 @@ class AscendCommonAttentionMetadata:
 
     slot_mapping_cpu: torch.Tensor
 
-    actual_seq_lengths_q: Optional[list[int]] = None
+    actual_seq_lengths_q: Optional[list[int]]
 
     positions: torch.Tensor = None