bench: rub it in — monsters, stdin wins, busybox retired

Suites split into benchmarks/files/{lines,words} and
benchmarks/stdin/piping, with the monsters bolted onto the lines suite:
100M lines raced against coreutils (~2x win), 1B lines solo (~6-8s,
11 GB in one pass). Stdin redirects from regular files are now mmap'd
in count_stream, so the stdin suite wins too — up to 12.00x on words.

The ratio column now reports how many times faster fastwc is, not how
much of GNU's time it used. busybox was removed from the suite: it
stopped being a challenge and started being a participation trophy.
GNU wc's lone win — 1M lines by one millisecond on hand-tuned AVX-512
assembly — is now a historical footnote, and the README says so.

STYLEGUIDE.md

@@ -54,7 +54,8 @@ product. The rest of the file is just the packaging.
   a mispredicted one is a lie you told the CPU.
 - **Regular files are mapped, not streamed.** The kernel hands us the
   pages; we count them, split across cores for anything past 8 MiB.
-  Stdin and odd files fall back to the `static`, 128 KiB buffer that
+  This includes stdin redirects from regular files. Real pipes, ttys,
+  and the `-m` path fall back to the `static`, 128 KiB buffer that
   never grows.
 
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