perf: socket server

[linrongbin16]

TODO: the manual testing is failed

I have no idea why TCP socket on 127.0.0.1:0 failed, the log shows serverstart is success, but sockconnect failed.

Maybe I should try pipe mode?

[linrongbin16]

Now I use the serverstart and sockconnect API to connect to the server inside nvim editor, it works, but it will break the running fzf terminal, so the UI looks like it blink.

That's really ugly, but for now it's the only solution I got.

---

Oh! I found I made a mistake, in previous debugging I use execute(...) in fzf options, now I revert it back to execute-silent(...) and everything is good now!

Also see wiki: https://github.com/linrongbin16/fzfx.nvim/wiki/How%3F#setup-socket-server-to-do-calculation-for-lua-scripts-executing-from-fzf

TODO: test on Windows.