Optional dependency on transformers

[DuarteMRAlves]

🚀 The feature, motivation and pitch

I want to utilize the liger-kernel fused operations on a codebase but do not need the requirement for transformers. However, when I import the liger_kernel.transformers package, it also imports the transformers library.

Alternatives

I can install transformers as a dependency, but it should not be required if it is not used.

Additional context

I understand that one of the goals of this project is the seamless drop in replacement for transformer models, but I believe it should be possible to import the operations without such a requirement.