v1.8.3 — the streaming cost table was wrong by a factor of a million

The table shipped in 1.8.2 read "$5,000–6,200 per 1M output tokens". The real figure is
$0.0050–0.0062 — the same digits with the decimal point six places out, from writing a
per-million-requests number into a per-million-tokens column.

1M output tokens × 280 µs        = 280,000 ms of CPU
280,000 ms × $0.02 per M CPU-ms  = $0.0056

Half a cent, against $0.60 of model charge for the same tokens.

Why it survived: the "~0.9% of the model bill" figure beside it was computed from the correct
per-request numbers and is unaffected. The ratio a reader would sanity-check against was right, and
only the absolute column was wrong, so the table read as internally consistent.

The corrected table carries CPU seconds as well as dollars, so the two check each other: 250–310
seconds of CPU per million output tokens, at $0.02 per million CPU-ms, cannot come to thousands of
dollars.

If you read 1.8.2's streaming section, re-read this one. Nothing else changed.

1251 offline tests pass.