xformers / flash attention

[M̵̞̗̝̼̅̏̎͝Ȯ̴̝̻̊̃̋̀Õ̷̼͋N̸̩̿͜ ̶̜̠̹̼̩͒]

Training is slow. We should do whatever we can to improve memory and training speed.