[Models] Improve iteration over layers (#19497)

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

vllm/model_executor/models/molmo.py

@@ -5,6 +5,7 @@ import math
 from collections.abc import Iterable, Mapping, Sequence
 from dataclasses import dataclass
 from functools import cached_property, partial
+from itertools import islice
 from typing import Annotated, Optional, Union
 
 import numpy as np
@@ -842,7 +843,7 @@ class MolmoModel(nn.Module, SupportsQuant):
             residual = intermediate_tensors["residual"]
 
         # Apply blocks one-by-one.
-        for layer in self.layers[self.start_layer:self.end_layer]:
+        for layer in islice(self.layers, self.start_layer, self.end_layer):
             hidden_states, residual = layer(
                 positions,
                 hidden_states,