uploading saffu language model to the transformers library
# What does this PR do?

In this PR, we upload a new language model **SAFFU** (Self-Attention-Feed-Forward-Unit) to the HuggingFace transformers library. This model is super efficient to use and fast to train that we derive a super efficient way of computing the self-attention matrix with an explicit mathematical solution.

Need to fix some issues of the code