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.

lib/io/io.ww

@@ -1,44 +1,26 @@
 // io — stream interface (Plan 9 Bio / Hare io::stream shape).
 //
-// No closures, no methods. A `stream` is a struct of function
-// pointers plus a `ctx: *void`. The error channel is the return
-// value of read/write/close — Hare-shaped tagged unions instead of
-// errno-style integer sentinels.
+// No closures, no methods. A `stream` is a pointer to a `vtable` of
+// function pointers (lib/io/stream.ww); read/write/close dispatch
+// through it. The error channel is the return value — Hare-shaped
+// tagged unions instead of errno-style integer sentinels.
+//
+// This file owns the eof / underread variant tags; lib/io/stream.ww
+// owns the `vtable` + `stream` + read/write/close dispatchers, and
+// lib/io/types.ww owns the error union, mode/whence enums, and the
+// reader/writer/closer fn-type aliases. #94 fold-eFinal collapsed the
+// pre-vtable `stream` struct + `closed` tag into the single vtable
+// surface; the dispatchers are read/write/close (over `stream`),
+// final over `handle` at io fold-2 (#5).
+package io;
 
 // eof — read past the end of the stream. Hare uses the `done`
 // singleton for EOF; ww doesn't have `done` yet so we ship a
-// named-void variant tag.
-package io;
-
+// named-void variant tag. Lifts to `done` with #93.
 export type eof = void;
 
-// closed — operation attempted on a stream that has already been
-// closed. ww-specific: Hare's io collapses this into the wider
-// errors union, but our stream vtable has no handle-ownership
-// semantics, so a distinct tag is honest. Named void.
-export type closed = void;
-
 // underread — an I/O handle hit eof partway through a fixed-size
 // read. Payload is the byte count actually delivered. Mirrors
 // Hare's `io::underread = !size`; ww uses i32 because the
 // underlying buffer-length type is i32 today.
 export type underread = !i32;
-
-export type stream = struct {
-	ctx:    *void,
-	read:   fn(s: *stream, buf: []u8) (i32 | eof | closed),
-	write:  fn(s: *stream, buf: []u8) (i32 | closed),
-	close:  fn(s: *stream) (void | closed),
-};
-
-export fn read(s: *stream, buf: []u8) (i32 | eof | closed) = {
-	return s.read(s, buf);
-};
-
-export fn write(s: *stream, buf: []u8) (i32 | closed) = {
-	return s.write(s, buf);
-};
-
-export fn close(s: *stream) (void | closed) = {
-	return s.close(s);
-};