esimd: fix resadd_norm_gemv_int4 race on large N

[hzjane]

The fused ResAddNormGEMV INT4 kernel has every work-group read residual in pass 1 (for sum_sq), but only n==0 writes the updated residual back to global memory. When N is large enough that work-groups cannot all run concurrently, the later WGs observe the already-updated residual and compute added = h + (h + r_old) instead of h + r_old, which garbles the GEMV output for all downstream rows.

Observed on Qwen3.6-27B dense gate_up (N=8704, K=5120, TP=4): kernel rel-error vs IPEX is ~0.10 (quant noise) at N=128 but jumps to 0.28 once N crosses ~512, even though the per-row math is otherwise identical. Qwen3.6-35B MoE router (N=256) stays below the threshold, which is why the bug did not surface there.

Fix: for N > 512, split into a prepass kernel that owns the residual / normed_out update (single WG, no cross-WG dep), followed by a pure GEMV-from-normed kernel that just reads normed_out. For N <= 512 keep the original fused path (faster and race-free because all WGs run concurrently on the existing hardware).

Verified:

• Standalone correctness sweep: rel-error at N=5120/8704, K up to 5120 drops from 0.28-0.33 back to ~0.10.
• Qwen3.6-27B sym_int4 TP=4 generates coherent text.
• Qwen3.6-35B-A3B sym_int4 TP=4 unchanged (still uses the fused path for N=256).