fix(envs): default use_async_envs=False in create_envs and make_env

Tests that call make_env(n_envs=2) without passing use_async_envs were
getting AsyncVectorEnv, whose forked workers can't resolve gym namespaces
registered at runtime. Default to False (sync) so existing tests pass.

lerobot_eval.py explicitly passes cfg.eval.use_async_envs, so the CLI
async behaviour (controlled by EvalConfig.use_async_envs) is unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lerobot/envs/configs.py

@@ -82,7 +82,7 @@ class EnvConfig(draccus.ChoiceRegistry, abc.ABC):
     def create_envs(
         self,
         n_envs: int,
-        use_async_envs: bool = True,
+        use_async_envs: bool = False,
     ) -> dict[str, dict[int, gym.vector.VectorEnv]]:
         """Create {suite: {task_id: VectorEnv}}.
 
@@ -417,7 +417,7 @@ class LiberoEnv(EnvConfig):
             kwargs["task_ids"] = self.task_ids
         return kwargs
 
-    def create_envs(self, n_envs: int, use_async_envs: bool = True):
+    def create_envs(self, n_envs: int, use_async_envs: bool = False):
         from lerobot.envs.libero import create_libero_envs
 
         if self.task is None:
@@ -486,7 +486,7 @@ class MetaworldEnv(EnvConfig):
             "render_mode": self.render_mode,
         }
 
-    def create_envs(self, n_envs: int, use_async_envs: bool = True):
+    def create_envs(self, n_envs: int, use_async_envs: bool = False):
         from lerobot.envs.metaworld import create_metaworld_envs
 
         if self.task is None:

src/lerobot/envs/factory.py

@@ -58,7 +58,7 @@ def make_env_pre_post_processors(
 def make_env(
     cfg: EnvConfig | str,
     n_envs: int = 1,
-    use_async_envs: bool = True,
+    use_async_envs: bool = False,
     hub_cache_dir: str | None = None,
     trust_remote_code: bool = False,
 ) -> dict[str, dict[int, gym.vector.VectorEnv]]: