import `torchvision` during Predict warmup (#13313)

ultralytics/nn/autobackend.py

@@ -620,6 +620,8 @@ class AutoBackend(nn.Module):
         Args:
             imgsz (tuple): The shape of the dummy input tensor in the format (batch_size, channels, height, width)
         """
+        import torchvision  # noqa (import here so torchvision import time not recorded in postprocess time)
+
         warmup_types = self.pt, self.jit, self.onnx, self.engine, self.saved_model, self.pb, self.triton, self.nn_module
         if any(warmup_types) and (self.device.type != "cpu" or self.triton):
             im = torch.empty(*imgsz, dtype=torch.half if self.fp16 else torch.float, device=self.device)  # input