feat: expanded fish configuration

Refactored fish configuration values into separate directory

Created fish init shell code for nh and zoxide

Reverted removal of cd=z alias since it works now

home-manager/stvnliu/shells/default.nix

@@ -9,7 +9,7 @@ in
   with lib; {
     imports = [
       ./zsh.nix
-      ./fish.nix
+      ./fish
       ./zoxide.nix
       ./direnv.nix
       ./starship