feat: use flake-parts to clean up the flake.nix

This is much more manageable!

flake-modules/overlays.nix

@@ -0,0 +1,26 @@
+{ inputs, ... }:
+{
+  # Add unstable packages to overlay
+  flake.overlays.unstable =
+    final: prev:
+    let
+      unstablePkgs = inputs.unstable.legacyPackages.${prev.stdenv.hostPlatform.system};
+    in
+    {
+      # Get unstable packages
+      unstable = unstablePkgs;
+
+      # Update vim plugins with the versions from unstable
+      vimPlugins = prev.vimPlugins // unstablePkgs.vimPlugins;
+
+      # Get specific packages from unstable
+      inherit (unstablePkgs)
+        gitoxide
+        jujutsu
+        neovim-unwrapped
+        ruff # nixpkgs stable version is improperly configured by nixvim
+        # wezterm
+        ;
+    };
+
+}