* sycl: Q4_K Weight unpack optimization and reuse between destination Columns
* sycl: Q4_K small N (N=2..4) + two output rows by subgroup reuse of activation between two rows.
* sycl: gate Q4_K two-row reuse for small N=2
* sycl: Fix on magic number now uses Q4_K_MMVQ_ROW_PAIR_MIN_NROWS=6272 for it, added tests for coverage around Q4_K_MMVQ_ROW_PAIR_MIN_NROWS with perf support to test Q4_K MUL_MAT, applied the same reuse pattern to the activation as the weights.
Assisted-by: GPT-5.6 Sol
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Co-authored-by: RaulAbejonDelgado <[email protected]>