* check in the two ways of approaching backwards for softcapping, both functional
* prepare the softcap switch for backwards
* temporary
* cleanup to the way Tri prefers
* calculate dtanh when copying from scores -> dtanh Tensor
* no ternary operators allowed for constexpr, so just use some hack found online
* fix maybe_dtanh, restore some files
* restore another file
* move calculate_dtanh to utils and colocate with apply_softcap
* cleanup
* maybe last cleanup
* save for another pr
* remove a stray line
* fix spacing
* fix an issue, and make test_flash_attn.py ready to test softcapping backwards
