First per-consumer step of stage 2b. n_ridx becomes a read-ahead pointer
leading the consume index by 1; bank_se read is registered into n_rd_data and
fed to ntt_core one cycle later (n_valid delayed 1 cyc). Cores hold ready_o
high through LOAD so a fixed 1-cycle skew suffices. Matches sd_bram registered
timing for this read port. 11/11 KAT PASS, byte-exact.