Refactor configs to have env in seperate yaml + Fix training

tests/test_datasets.py

@@ -0,0 +1,17 @@
+import pytest
+
+from lerobot.common.datasets.factory import make_offline_buffer
+
+from .utils import init_config
+
+
+@pytest.mark.parametrize(
+    "env_name",
+    [
+        "simxarm",
+        "pusht",
+    ],
+)
+def test_factory(env_name):
+    cfg = init_config(overrides=[f"env={env_name}"])
+    offline_buffer = make_offline_buffer(cfg)