[Models] Improve iteration over layers (#19497)

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

vllm/model_executor/models/step3_text.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 """Inference-only Jurassic model."""
 from collections.abc import Iterable
+from itertools import islice
 from typing import Any, Optional
 
 import torch
@@ -346,8 +347,7 @@ class Step3TextModel(nn.Module):
             hidden_states = intermediate_tensors["hidden_states"]
             residual = intermediate_tensors["residual"]
 
-        for i in range(self.start_layer, self.end_layer):
-            layer = self.layers[i]
+        for layer in islice(self.layers, self.start_layer, self.end_layer):
             hidden_states, residual = layer(positions, hidden_states, residual)
 
         if not get_pp_group().is_last_rank: