refactor(envs): remove __del__ from _LazyAsyncVectorEnv

__del__ is unreliable as a cleanup mechanism. close() is already called
explicitly in the eval loop's finally block, so the finalizer is redundant.

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

src/lerobot/envs/libero.py

@@ -458,9 +458,6 @@ class _LazyAsyncVectorEnv:
             self._env.close()
             self._env = None
 
-    def __del__(self):
-        self.close()
-
 
 # ---- Main API ----------------------------------------------------------------