v1.8.1 — the price tables now follow the CPU table

Documentation and measurement rig only. No behaviour change.

The cost table was replaced in 1.8.0 with a clean measurement. The two dollar tables downstream of it
were not, so the README quoted 118.3 ms and 104 ms for the same row in two places and priced a
billion 4 MB requests off superseded numbers. Both are now derived from the CPU table and nothing
else, and the section says so.

The per-option table is rebased onto the current 51.5 ms baseline. Its deltas were always measured as
CPU differences and are unchanged; only the absolute dollars moved.

Also lands the measurement ops that produced 1.7.0 and 1.8.0, which were live on the edge but never
committed — including the real-socket depth ladder, which is the only decomposition here that turned
out to be trustworthy: against it the isolated benches under-price the record layer by 14× and
over-price HTTP/2 by 2×.

1251 offline tests pass.