[Mypy] Fix mypy for vllm/model_executor (except vllm/model_executor/layers) (#37904)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

vllm/model_executor/layers/sparse_attn_indexer.py

@@ -96,6 +96,7 @@ def sparse_attn_indexer(
     topk_indices_buffer[: hidden_states.shape[0]] = -1
     if has_prefill:
         prefill_metadata = attn_metadata.prefill
+        assert prefill_metadata is not None
 
         # Get the full shared workspace buffers once (will allocate on first use)
         workspace_manager = current_workspace_manager()
@@ -170,6 +171,8 @@ def sparse_attn_indexer(
 
     if has_decode:
         decode_metadata = attn_metadata.decode
+        assert decode_metadata is not None
+        # kv_cache shape [
         # kv_cache size requirement [num_block, block_size, n_head, head_dim],
         # we only have [num_block, block_size, head_dim],
         kv_cache = kv_cache.unsqueeze(-2)