Make the _get_state function more Pythonic and concise

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: SamanehSaadat

guides/orbax_checkpoint.py

@@ -81,14 +81,8 @@ def __init__(
 
     def _get_state(self):
         """Gets the model state and metrics"""
-        model_state = self._model.get_state_tree()
-        state = {}
-        metrics = None
-        for k, v in model_state.items():
-            if k == "metrics_variables":
-                metrics = v
-            else:
-                state[k] = v
+        state = self._model.get_state_tree().copy()
+        metrics = state.pop("metrics_variables", None)
         return state, metrics
 
     def save_state(self, epoch):