[Cute] Add block-sparsity support to SM100

- Implement block-sparse attention in flash_fwd_sm100.py
- Update interface.py to handle SM100 block size calculations
  (2x multiplier for m_block_size since 1 CTA handles 2*tile_m rows)
- Add mask_mod parameter support in mask.py for block-sparse masking
- Add SM100 test fixtures and tile size handling in test_mask_mod.py

This enables block-sparsity on SM 10.0 architecture, including
mask_mod support and proper block size accounting.

Author: drisspg