[Example] Add sparse gqa decode example (#332)

* add example gqa decode wgmma pipelined

* add sparse gqa

* support num split

* support num split

* add if condition

* add heuristic num split

* clean code

* add ref

* fix bug

* add torch ref

* fix bug

* integrate to torch

* symbolic

* clean mask

* rm actual_num_blocks

* clean code

* get num_sm via torch

* add sparse gqa decode example

* format

* rm example_gqa_decode_wgmma_pipelined.py

* Add license headers to example scripts

* format

* Remove commented-out cache disabling lines

---------
Co-authored-by: Lei Wang <34334180+LeiWang1999@users.noreply.github.com>

examples/flash_decoding/heuristic.py → examples/blocksparse_attention/heuristic.py

@@ -21,7 +21,6 @@ def num_splits_heuristic(total_mblocks, num_SMs, num_n_blocks, num_m_blocks, siz
     # If we have enough m_blocks to almost fill the SMs, prefer 1 split unless memory constraints apply.
     if total_mblocks >= 0.8 * num_SMs:
         size_l2 = 50 * 1024 * 1024  # L2 cache size assumption (50MB)
-
         # Only split if each KV head is too large for L2 and there are enough m_blocks
         if size_one_kv_head > size_l2 and num_m_blocks >= num_SMs * 2 and not is_causal_or_local:
             return min((size_one_kv_head + size_l2 - 1) // size_l2, max_splits)
@@ -42,7 +41,6 @@ def num_splits_heuristic(total_mblocks, num_SMs, num_n_blocks, num_m_blocks, siz
     for num_splits in range(1, max_splits + 1):
         n_waves = (total_mblocks * num_splits) / num_SMs
         eff = n_waves / math.ceil(n_waves)
-
         # Track max efficiency
         if eff > max_efficiency:
             max_efficiency = eff