Replace the hand-rolled multiplexer (internal/mux) with xtaci/smux v2
running on top of the existing KCP-reliable vp8channel transport.
- Add internal/muxconn: io.ReadWriteCloser adapter bridging link.Link
(message-oriented) into the byte-stream smux expects; applies AEAD
on every write and inverts it on every received message
- Rewrite client: smux.Client session over muxconn; OpenStream per
SOCKS5 connection; reconnect handler tears down and rebuilds session
- Rewrite server: smux.Server session; AcceptStream loop dispatches
each stream to a proxy handler; tolerates session bounces on reconnect
- Delete internal/mux: all sequence/reorder/buffer logic is now
handled by smux + KCP
zarazaex69