lib: collapse the parallel vstream scaffold onto the single Hare io surface (#94 fold-eFinal)

The Option-C parallel _v vstream API was scaffolding to bring the io stack up alongside the old surface; carrying both permanently is a rule-9 divergence from ref/hare, which has exactly one io surface. Collapse onto that surface (stream = *vtable, ref/hare/io/stream.ha) and rename the _v symbols to their Hare names (io vstream->stream, fmt vfprint->fprint, bufio/memio/log surfaces, log.new). Deletes the 4 lib/*/vstream.ww scaffold files; regenerates w6c/wwdump combined.ww. cstage and wwstage stay byte-identical and combined_ww_fresh holds; all 220 tests pass.

test/wcc/900_stdlib.c

@@ -34,7 +34,7 @@ static const char *modules[] = {
 	 * lib/os/os.ww, and lib/strings/strings.ww moved off this list:
 	 * each has cross-module type refs that only resolve once the
 	 * driver concatenates `use`d modules. bufio / fmt graduated to
-	 * io.stream-based sinks (*io.stream, io.closed, io.eof); lib/os
+	 * io.stream-based sinks (io.stream = *io.vtable, io.eof, io.error); lib/os
 	 * carries time.instant in filestat post-Commit B;
 	 * lib/strings.iterator + lib/strings.next reference utf8.decoder
 	 * / utf8.done; lib/bytes.tokenize references os.assert +