Process two independent SHA256 chains simultaneously to hide the 2-cycle
latency of vsha256hq_u32 on Cortex-A76, approaching full throughput.
Also reduces memcpy from 512 to ~192 bytes per 4-nonce group by reusing
block buffers, and adds scan_4way_direct to bypass pthread_once (LDAR
barrier) on every inner-loop call.
add local Codex skill for Python->C performance-focused translation
define modular C architecture and benchmark/correctness gates
add references for patterns, profiling, and module design
add scaffold_c_module.py to generate include/src/tests/bench skeleton
update agent default prompt for benchmark-backed optimizations
