Renames dzero_hold to dzoh and adds column stride

[LoserCheems]

Shortens variable names for better readability and consistency.

Adds missing column stride parameter to support proper memory layout handling.

[Copilot]

Pull Request Overview

This PR refactors parameter names for backward pass buffers and adds support for column stride in the Flash_bwd_params struct.

• Shortens dzero_hold member names to dzoh for pointers and strides.
• Introduces dzoh_col_stride to handle column-major memory layouts.

Comments suppressed due to low confidence (3)

csrc/src/flash.h:168

• [nitpick] The abbreviation dzoh may be unclear to new readers; consider expanding it (e.g., d_zero_hold_ptr) or adding a brief comment explaining the contraction for maintainability.

    void *__restrict__ dzoh_ptr;

csrc/src/flash.h:198

• Add a comment or docstring explaining the purpose and usage of dzoh_col_stride to ensure clarity for future maintainers.

    index_t dzoh_col_stride;

csrc/src/flash.h:198

• Introduce or update unit tests to cover the newly added dzoh_col_stride behavior to prevent regressions in memory layout assumptions.

    index_t dzoh_col_stride;