Make sure init_hydra_config does not require any keys (#376)

lerobot/scripts/eval.py

@@ -454,6 +454,16 @@ def main(
     else:
         hydra_cfg = init_hydra_config(hydra_cfg_path, config_overrides)
 
+    if hydra_cfg.eval.batch_size > hydra_cfg.eval.n_episodes:
+        raise ValueError(
+            "The eval batch size is greater than the number of eval episodes "
+            f"({hydra_cfg.eval.batch_size} > {hydra_cfg.eval.n_episodes}). As a result, {hydra_cfg.eval.batch_size} "
+            f"eval environments will be instantiated, but only {hydra_cfg.eval.n_episodes} will be used. "
+            "This might significantly slow down evaluation. To fix this, you should update your command "
+            f"to increase the number of episodes to match the batch size (e.g. `eval.n_episodes={hydra_cfg.eval.batch_size}`), "
+            f"or lower the batch size (e.g. `eval.batch_size={hydra_cfg.eval.n_episodes}`)."
+        )
+
     if out_dir is None:
         out_dir = f"outputs/eval/{dt.now().strftime('%Y-%m-%d/%H-%M-%S')}_{hydra_cfg.env.name}_{hydra_cfg.policy.name}"