style: Added annotation typing for alexnet (#2859)

torchvision/models/alexnet.py

 import torch
 import torch.nn as nn
 from .utils import load_state_dict_from_url
+from typing import Any
 
 
 __all__ = ['AlexNet', 'alexnet']
@@ -13,7 +14,7 @@ model_urls = {
 
 class AlexNet(nn.Module):
 
-    def __init__(self, num_classes=1000):
+    def __init__(self, num_classes: int = 1000):
         super(AlexNet, self).__init__()
         self.features = nn.Sequential(
             nn.Conv2d(3, 64, kernel_size=11, stride=4, padding=2),
@@ -41,7 +42,7 @@ class AlexNet(nn.Module):
             nn.Linear(4096, num_classes),
         )
 
-    def forward(self, x):
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
         x = self.features(x)
         x = self.avgpool(x)
         x = torch.flatten(x, 1)
@@ -49,7 +50,7 @@ class AlexNet(nn.Module):
         return x
 
 
-def alexnet(pretrained=False, progress=True, **kwargs):
+def alexnet(pretrained: bool = False, progress: bool = True, **kwargs: Any) -> AlexNet:
     r"""AlexNet model architecture from the
     `"One weird trick..." <https://arxiv.org/abs/1404.5997>`_ paper.