[booster] implemented the torch ddd + resnet example (#3232)

* [booster] implemented the torch ddd + resnet example

* polish code

colossalai/interface/model.py

@@ -0,0 +1,25 @@
+import torch.nn as nn
+
+
+class ModelWrapper(nn.Module):
+    """
+    A wrapper class to define the common interface used by booster.
+
+    Args:
+        module (nn.Module): The model to be wrapped.
+    """
+
+    def __init__(self, module: nn.Module) -> None:
+        super().__init__()
+        self.module = module
+
+    def unwrap(self):
+        """
+        Unwrap the model to return the original model for checkpoint saving/loading.
+        """
+        if isinstance(self.module, ModelWrapper):
+            return self.module.unwrap()
+        return self.module
+
+    def forward(self, *args, **kwargs):
+        return self.module(*args, **kwargs)