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Co-authored-by: Ntianhaodongbd <tianhaodong@baidu.com>

* add mask

* add backword

* add enforce info

* update scale

* integrate code

* update enforce

* add enforce eq

* add error type

* update enforce

* add test_flash_attention

* Polish codes and fix compiling errors.

* Set num_splits to 0 for flash-attn with tensor mask.

* Fix the compiling error for non flash-attn case.

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Co-authored-by: NLiu Yiqun <liuyiqun01@baidu.com>

* add flash randomness control

* fix VLOG undefied

* fix flash attn

* fix another API

* rename flash_attn_raw to flash_attn_unpadded

* fix static api

* fix static return

* flash attn

* seed

* almost

* softmax

* fix workspace

* add unitest; linux only

* fix setup

* fix datatype include

* fix setup typo

* fix def scope

* new error api

* use paddle fork

* fix attr bug; complete ut

* update flash hash

* fix rng reset

* fix offset

* fix comments