portfwdserver: consolidate `bicopy` and `tcpproxy` packages into one

[AkihiroSuda]

lima/pkg/portfwdserver/server.go

Lines 44 to 58 in 83cbc02

	// FIXME: consolidate bicopy and tcpproxy into one
	//
	// The bicopy package does not seem to work with `w3m -dump`:
	// https://github.com/lima-vm/lima/issues/3685
	//
	// However, the tcpproxy package can't pass the CI for WSL2 (experimental):
	// https://github.com/lima-vm/lima/pull/3686#issuecomment-3034842616
	if wsl2, _ := seemsWSL2(); wsl2 {
	bicopy.Bicopy(rw, conn, nil)
	} else {
	proxy := tcpproxy.DialProxy{DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
	return conn, nil
	}}
	proxy.HandleConn(rw)
	}

[nirs]

Did we try with upstream tcpproxy? the givisor version is not the same.

Upstream version does:

1. Start io.Copy(src, dst)
2. Start io.Copy(dst, src)
3. When io.Copy() finish, do CloseWrite(dst) and CloseRead(src)
4. Wait until both io.Copy finish
5. Close src and dst

givisor version does:

1. Start io.Copy(src, dst)
2. Start io.Copy(dst, src)
3. Wait until first io.Copy finish
4. Close src and dst