feat(flake): clean up & simplify config

- remove unused wrappers
- improve packages & overlays setup
- simplify createSystem

pkgs/vim-plugins/default.nix

@@ -0,0 +1,6 @@
+{ inputs, pkgs, ... }:
+
+{
+  nvim-kitty-navigator =
+    pkgs.callPackage ./nvim-kitty-navigator { inherit inputs; };
+}

pkgs/vim-plugins/nvim-kitty-navigator/default.nix

@@ -0,0 +1,8 @@
+{ inputs, pkgs, ... }:
+
+pkgs.vimUtils.buildVimPluginFrom2Nix {
+  pname = "nvim-kitty-navigator";
+  version = inputs.nvim-kitty-navigator.rev;
+  versionSuffix = "-git";
+  src = inputs.nvim-kitty-navigator;
+}