v1.4.2: Cleanup model arguments (#102)

* added attn_implementation to the model arguments

* added a check on the concept_value

* set None unit to a default value N/A

* set None value in concept_values to 0.0

* set _supports_sdpa = True in BertPreTrainedModel

* implemented flash attn

* do not overwrite the attention mask when flash attention is enabled

* upgraded huggingface transformers

* updated the logic for splitting heads

* make sure we load the model using the specified torch_dtype

* set the entire model to the corresponding dtype

* removed keyward arguments from hf_cehrgpt

* updated BertSelfFlashAttention.forward to return a tuple because the BERT layer expects such output

* test gpt2 implementation

* test gpt2 implementation

* pass the attn_implementation and torch_dtype to the model during fine-tuning

* set the default value of torch_dtype to auto

* convert age_at_index to the same data type as the bert output

* added logic to convert float32 to the corresponding precision

* removed mlm_skip_values

* updated the unit test after removing mlm_skip_values

* set the default value of torch_dtype to None

* convert concept_value_masks to torch.bool before using it in torch.where

* convert tensors back to the original dtype in the flash attention implementation

* check if torch_dtype is null before trying to get it from torch