[Models] Improve iteration over layers (#26425)

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

vllm/model_executor/models/mamba.py

@@ -3,6 +3,7 @@
 """PyTorch MAMBA model."""
 
 from collections.abc import Iterable
+from itertools import islice
 from typing import Optional
 
 import torch
@@ -162,8 +163,7 @@ class MambaModel(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=positions, hidden_states=hidden_states, residual=residual
             )