feat: adopt flakes

I was trying to contribute to nc4nix but prefer flakes. Flakes make this even more reproducable. I "flakified" the repo with gomod2nix. The update removed ` delve libcap` from shell.nix , but `go build` works without it ? The stuff in default.nix I am not sure what it's about I dont develop in go, `go run` seemed like the good command to start nc4nix but it does nothing both on main and in this branch ?