fix: replace HybridCache with Cache in gemma2 and gemma3

[qgallouedec]

HybridCache has been deprecated, and is now removed, see huggingface/transformers#43168, causing

  trl/trainer/dpo_trainer.py:500: in __init__
      super().__init__(
  .venv/lib/python3.12/site-packages/transformers/trainer.py:479: in __init__
      from liger_kernel.transformers import _apply_liger_kernel_to_instance
  .venv/lib/python3.12/site-packages/liger_kernel/transformers/__init__.py:140: in __getattr__
      module = importlib.import_module("liger_kernel.transformers.monkey_patch")
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  /__w/_tool/Python/3.12.12/x64/lib/python3.12/importlib/__init__.py:90: in import_module
      return _bootstrap._gcd_import(name[level:], package, level)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  .venv/lib/python3.12/site-packages/liger_kernel/transformers/monkey_patch.py:21: in <module>
      from liger_kernel.transformers.model.gemma2 import lce_forward as gemma2_lce_forward
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
  
      import logging
      
      from typing import Optional
      from typing import Tuple
      from typing import Union
      
      import torch
      
      from torch.nn import CrossEntropyLoss
  >   from transformers.cache_utils import HybridCache
  E   ImportError: cannot import name 'HybridCache' from 'transformers.cache_utils' (/__w/trl/trl/.venv/lib/python3.12/site-packages/transformers/cache_utils.py)
  
  .venv/lib/python3.12/site-packages/liger_kernel/transformers/model/gemma2.py:10: ImportError

This PR fixes this issue

[Tcc0403]

Thank you!