Fix crash when trl.experimental.openenv is unavailable (#3787)

* Guard optional trl.experimental.openenv usage in RL patches

* Simplify optional trl.openenv import handling

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

unsloth/models/rl_replacements.py

@@ -949,11 +949,15 @@ def openenv_vllm_reload_weights():
         return
     if Version(importlib_version("trl")) < Version("0.26.0"):
         return
+
     try:
         import trl.experimental.openenv.utils as openenv_utils
         import trl.experimental.openenv as openenv
     except ImportError as e:
         logger.info(f"Unsloth: Failed to import trl openenv: {e}")
+        logger.info(
+            "Unsloth: trl.experimental.openenv not available — skipping RL openenv patches."
+        )
         return
 
     src = inspect.getsource(openenv_utils.generate_rollout_completions)