[Models] Improve iteration over layers (#19497)

Signed-off-by: Lukas Geiger <lukas.geiger94@gmail.com>

vllm/model_executor/models/qwen2.py

@@ -25,6 +25,7 @@
 # limitations under the License.
 """Inference-only Qwen2 model compatible with HuggingFace weights."""
 from collections.abc import Iterable
+from itertools import islice
 from typing import Any, Optional, Union
 
 import torch
@@ -358,7 +359,7 @@ class Qwen2Model(nn.Module):
 
         aux_hidden_states = []
         for idx, layer in enumerate(
-                self.layers[self.start_layer:self.end_layer]):
+                islice(self.layers, self.start_layer, self.end_layer)):
             if idx in self.aux_hidden_state_layers:
                 aux_hidden_states.append(hidden_states + residual)
             hidden_states, residual = layer(positions, hidden_states, residual)