feat: nixvim refactor

modules/home-manager/programs/nixvim/presets/languages/nix.nix

@@ -0,0 +1,23 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}:
+let
+  cfg = config.presets.languages.nix;
+in
+{
+  options.presets.languages.nix = {
+    enable = lib.mkEnableOption "Nix";
+  };
+
+  config = lib.mkIf cfg.enable {
+    plugins = {
+      conform-nvim.formattersByFt.nix = [ "nixfmt" ];
+      lsp.servers.nil_ls.enable = true;
+      nix.enable = true;
+    };
+    extraPackages = [ pkgs.nixfmt-rfc-style ];
+  };
+}