fix(utils): add missing importlib import to fix NameError (#2134)

This commit fixes a NameError that occurs when `importlib` is referenced in _utils.py
without being imported, especially when UNSLOTH_USE_MODELSCOPE=1 is enabled.
By adding the missing import statement, the code will no longer throw a NameError.

Author: naliazheli

unsloth/models/_utils.py

@@ -1243,6 +1243,7 @@ def __str__ (self): return LOGITS_ERROR_STRING
         except: continue
 pass
 
+import importlib
 USE_MODELSCOPE = os.environ.get("UNSLOTH_USE_MODELSCOPE", "0") == "1"
 if USE_MODELSCOPE:
     if importlib.util.find_spec("modelscope") is None: