debug: 固定验证集上的随机噪声，修复resnet在训练时bn层会切换到train的问题

roboimi/vla/models/backbones/resnet.py

@@ -27,6 +27,16 @@ class ResNetBackbone(VLABackbone):
             param.requires_grad = False
         self.model.eval()
 
+    def train(self, mode=True):
+        """
+        Override train() to keep frozen ResNet in eval mode.
+        This ensures BatchNorm layers use running statistics consistently.
+        """
+        super().train(mode)
+        if hasattr(self, 'model'):
+            self.model.eval()  # Always keep ResNet in eval mode
+        return self
+
     def forward_single_image(self, image):
         B, T, C, H, W = image.shape
         image = image.view(B * T, C, H, W)