ring-flash-attention

Merge pull request #34 from Yuxin-CV/improve_update_out_and_lse

add descriptive comments to `_update_out_and_lse` to clarify its computational logic.

Merge pull request #32 from Yuxin-CV/set_seed

improve readability and potential numerical stability of `out` and `lse` in `_update_out_and_lse` by refactoring their computational expressions.

fix random seed in test files for reproducibility