class_docstr: Mask IoU Head.
  
  This head predicts the IoU of predicted masks and corresponding gt masks.
code: def forward(self, mask_feat, mask_pred):
      mask_pred = mask_pred.sigmoid()
      mask_pred_pooled = self.max_pool(mask_pred.unsqueeze(1))
  
      x = torch.cat((mask_feat, mask_pred_pooled), 1)
  
      for conv in self.convs:
          x = self.relu(conv(x))
      x = x.flatten(1)
      for fc in self.fcs:
          x = self.relu(fc(x))
      mask_iou = self.fc_mask_iou(x)
      return mask_iou
  
file_path: insightface/detection/scrfd/mmdet/models/roi_heads/mask_heads/maskiou_head.py
imports: import numpy
  import torch
  import torch.nn
  from mmcv.cnn import Conv2d, Linear, MaxPool2d, kaiming_init, normal_init
  from mmcv.runner import force_fp32
  from torch.nn.modules.utils import _pair
  from mmdet.models.builder import HEADS, build_loss
label_desc: Use image node_id 3 for calling the MaskIoUHead obj's underlying member method code with example usage: obj.forward(mask_feat, mask_pred) and returns: mask_iou