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/types.ww

@@ -1,19 +1,17 @@
 // types — error union, mode/whence enums, reader/writer/closer
-// fn-type aliases. Project #94 fold-1 step (d) (drew Fold D); the
-// fn-aliases re-targeted from *stream → vstream as part of fold-e1
-// (vtable port in stream.ww).
+// fn-type aliases. Project #94 fold-eFinal; the fn-aliases target
+// `stream` (= `*vtable`, the single io surface).
 //
 // Hare splits the io module across stream.ha + types.ha and ww does
-// the same: lib/io/io.ww owns the (pre-vtable) `stream`, `eof`, and
-// `underread` shapes; lib/io/stream.ww owns the Hare vtable port
-// (`vtable`, `vstream`, `st_read`/`st_write`/`st_close` dispatch);
-// this file owns the surrounding port. The three files share
-// `package io;` so cross-file refs resolve via the dir-enum concat
-// order (io.ww < stream.ww < types.ww — `vstream` lands before the
-// reader/writer/closer aliases below).
+// the same: lib/io/io.ww owns the `eof` and `underread` tags;
+// lib/io/stream.ww owns the vtable surface (`vtable`, `stream`,
+// `read`/`write`/`close` dispatch); this file owns the surrounding
+// port. The three files share `package io;` so cross-file refs
+// resolve via the dir-enum concat order (io.ww < stream.ww < types.ww
+// — `stream` lands before the reader/writer/closer aliases below).
 //
 // Deferrals (drew-signed): `handle`, `seeker`, `copier`, `strerror`
-// land with fold-e2+ (need the `handle` sum). Hare's `EOF = done`
+// land with io fold-2 (#5; need the `handle` sum). Hare's `EOF = done`
 // stays as `io.eof` until the `done` singleton ships (#93).
 
 package io;
@@ -43,20 +41,20 @@ export type whence = enum i32 {
 // ww enumerates the tags explicitly (ken's #204-block — spread of an
 // errors-side tagged into this union triggers a wrapper-vs-flatten
 // layout mismatch; #199b layout-extension is the deferred fix). The
-// st_read/st_write dispatchers in stream.ww return
-// `errors.unsupported` when the matching vtable slot is unset, so the
-// variant lands here directly.
+// read/write dispatchers in stream.ww return `errors.unsupported`
+// when the matching vtable slot is unset, so the variant lands here
+// directly.
 export type error = !(errors.unsupported | underread | nomem);
 
-// ref/hare/io/types.ha:46. `eof` (not Hare's `done`) per the io.ww:8
-// rationale; lifts to `done` with #93. `vstream` forward-refs the
+// ref/hare/io/types.ha:46. `eof` (not Hare's `done`) per the io.ww
+// rationale; lifts to `done` with #93. `stream` forward-refs the
 // `*vtable` alias in stream.ww — the dispatcher receives the vtable
 // pointer directly (Hare's stream.ha:33 + types.ha:46 collapse).
-export type reader = fn(s: vstream, buf: []u8) (size | eof | error);
+export type reader = fn(s: stream, buf: []u8) (size | eof | error);
 
 // ref/hare/io/types.ha:51. No `const` qualifier — ww has none, and
-// lib/io/io.ww:30 + lib/sort/sort.ww:18 drop it the same way.
-export type writer = fn(s: vstream, buf: []u8) (size | error);
+// lib/sort/sort.ww:18 drops it the same way.
+export type writer = fn(s: stream, buf: []u8) (size | error);
 
 // ref/hare/io/types.ha:55.
-export type closer = fn(s: vstream) (void | error);
+export type closer = fn(s: stream) (void | error);