fix(deps): constrain Transformers compatibility

[KartikP]

Summary

• require Transformers 4.51 or newer for DynamicCache and Qwen3 support
• exclude Transformers 5, which removed the cache conversion APIs
• keep Hugging Face Hub below 1.0 through the Transformers 4 dependency range so datasets 2.x remains compatible

Testing

• resolved the Linux Python 3.11 dependency graph to Transformers 4.57.6 and Hugging Face Hub 0.36.2
• built the wheel and verified Requires-Dist: transformers<5,>=4.51