hrx: reuse Q6 row64 tile coordinates in tiled prefill - #189

Overview

Pass the already computed tile and local row into Q6 row64 tiled dequantization, avoiding repeated coordinate arithmetic. Other callers keep their existing wrapper.

This is fix 3/5 in the row64 stack following #181. Stacks on #188; base branch: users/astgeorg/row64-q6-known-row. Commit: d36ffbf878e950963147cfd6350b65149e23023c. Keep each fix as a separate stacked PR.

Validation

Clean committed build and five focused controls passed. Exact nonzero Q6 tiled output matches its immediate parent byte for byte; its inherited strict-reference failure remains. Review with the final hint-localization fix, which preserves shared decode code generation.

The complete stack at bd85479285423b239213519d0892c56d071864df was measured against frozen integration be335351871563a09520b0db4a63c21db2040807 with standalone llama-bench. The final fifteen-model table and separate Qwen3-0.6B stability result are in #181; those combined-stack results are not isolated gains from this commit.

Requirements

• Contributing guidelines reviewed for this fork; human review and acceptance remain pending.
• AI usage disclosure: YES. Codex assisted implementation, validation, independent review and this description under the user's direction.