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

[AkihiroSuda]

https://github.com/lima-vm/lima/blob/83cbc0262baeb8b1ce0407094a53f3ad90aa7a84/pkg/portfwdserver/server.go#L44-L58

[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

[norio-nomura]

I'm changing tcpproxy to https://github.com/inetaf/tcpproxy in #4175

[norio-nomura]

It changed to use "github.com/containers/gvisor-tap-vsock/pkg/tcpproxy" by #4237. I benchmarked by using:

• github.com/containers/gvisor-tap-vsock/pkg/tcpproxy
• github.com/inetaf/tcpproxy
• github.com/lima-vm/lima/v2/pkg/bicopy

However, there was no big difference, so I used gvisor-tap-vsock's tcpproxy as it is.