added podman and shortcut for nixos rebuilds

modules/core/nix.nix

@@ -1,4 +1,4 @@
-{ ... }:
+{ inputs, ... }:
 
 {
   nix = {
@@ -20,4 +20,13 @@
   };
 
   nixpkgs.config.allowUnfree = true;
+
+  nixpkgs.overlays = [
+    (final: prev: {
+      unstable = import inputs.nixpkgs-unstable {
+        inherit (prev) system;
+        inherit (prev) config;
+      };
+    })
+  ];
 }