chore: move constants to utils (#2016)

tests/optim/test_optimizers.py

@@ -14,10 +14,6 @@
 import pytest
 import torch
 
-from lerobot.constants import (
-    OPTIMIZER_PARAM_GROUPS,
-    OPTIMIZER_STATE,
-)
 from lerobot.optim.optimizers import (
     AdamConfig,
     AdamWConfig,
@@ -26,6 +22,10 @@ from lerobot.optim.optimizers import (
     load_optimizer_state,
     save_optimizer_state,
 )
+from lerobot.utils.constants import (
+    OPTIMIZER_PARAM_GROUPS,
+    OPTIMIZER_STATE,
+)
 
 
 @pytest.mark.parametrize(