Block Sparsity and Flex Attention mask mod support (#1942)

* clean up and rebase for PR

* add mask mod tests

* add benchmarking files

* refactor for better style

* remove extraneous csrc

* type hint buffers

* refactor: order of non/overlap and modify blocksparse producer to agree with dense

* change variable name back to buffers

* remove unnecessary variable in first_half_block

* restore erroneous packgqa deletion

* add blocksparsity and mask_mod asserts to interface.py

* fix rebase issues

* Restore submodule and reset pointer to upstream/main

* rename cutlass.const_expr to const_expr

* support fully masked m blocks (i.e. skipped tiles)

* remove outdated commented code