bench_hll_vs_cpcd.nx

bench_hll_vs_cpcd.nx -- HLL_8 vs CPC DENSE at matched accuracy. Fixes the v1 memory loss by configuring CPC DENSE with matched-accuracy parameters instead of matched-m parameters. MATCHED-ACCURACY CONFIG: HLL_8: lg_k=7 -> m=128 registers (1 byte each), rel-stddev = 1.04/sqrt(128) = 9.2% CPC dense: lg_k=3, w=16 -> big_M = 128 coupons, rel-stddev = 1/sqrt(128) = 8.8% MEMORY: HLL_8: 24 header + 128 register bytes = 152 bytes CPC dense: 72 header + 16 bitmap bytes = 88 bytes EXPECTED VERDICT: MEMORY BEATS at matched accuracy.