Fix/transformers v5 gemma tokenizer

[daiyunwei1998]

Summary

Update Gemma tokenizer usage in convergence tests for Transformers v5 by removing deprecated GemmaTokenizerFast imports and renaming usages to the supported non-fast tokenizer class. This fixes the No module named transformers.models.gemma.tokenization_gemma_fast error when running convergence tests under Transformers v5.

Details

Transformers v5 moves away from parallel “fast” and “slow” tokenizer implementations and adopts a single tokenizer implementation (see huggingface/transformers#40936).

• Convergence tests were importing and instantiating the fast tokenizer class, causing import errors.
• This change updates both: 1) the import path, and 2) the tokenizer class name used in code (GemmaTokenizerFast → GemmaTokenizer), following the new Transformers v5 API.

Testing Done

• Hardware Type: A100-40G-PCIe
• run make test to ensure correctness
• run make checkstyle to ensure code style
• run make test-convergence to ensure convergence

[Tcc0403]

LGTM, thank you!