[CuTe DSL] Update "buffers" name to "aux_tensors"; fix flex bugs (#1961)

* 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* remove outdated commented code

* rename buffers -> aux_tensors, fix score_mod test in sm90 fwd

* fix mask mod interface issues and tests

* remove newline at end of file

* format with ruff

* format mask & sm100 with ruff

* format more files with ruff

* format barrier.py with ruff