feat: blocksparse support

[guangyunh-nv]

This is still a wip and needs further cleanup and refactor.

This currently builds with

export FLASH_ATTENTION_DISABLE_SPLIT="TRUE"
export FLASH_ATTENTION_DISABLE_APPENDKV="TRUE"
export FLASH_ATTENTION_DISABLE_LOCAL="TRUE"
export FLASH_ATTENTION_DISABLE_PACKGQA="TRUE"
export FLASH_ATTENTION_DISABLE_PAGEDKV="TRUE"
export FLASH_ATTENTION_DISABLE_HDIM64="TRUE"
export FLASH_ATTENTION_DISABLE_HDIM96="TRUE"
export FLASH_ATTENTION_DISABLE_HDIM192="TRUE"
export FLASH_ATTENTION_DISABLE_HDIM256="TRUE"
export FLASH_ATTENTION_DISABLE_SM80="TRUE"

export MAX_JOBS=16

cd hopper
pip install --verbose --no-build-isolation -e .