use some unstable pkgs, reorganize hw

modules/nixpkgs.nix

@@ -1,6 +1,17 @@
-{...}: {
+{config, ...}: let
+  unstable-commit-sha = "f5892ddac112a1e9b3612c39af1b72987ee5783a";
+in {
   config = {
-    nixpkgs.config.allowUnfree = true;
+    nixpkgs.config = {
+      allowUnfree = true;
+
+      # make nixos-unstable availiable as 'pkgs.unstable'
+      packageOverrides = pkgs: {
+        unstable = import (fetchTarball "https://github.com/nixos/nixpkgs/tarball/${unstable-commit-sha}") {
+          config = config.nixpkgs.config;
+        };
+      };
+    };
 
     system = {
       stateVersion = "22.11";