Update helium to 0.14.3.1 and add fastfetch alias

- Bump nixpkgs lock to a newer revision with updated hash.
- Disable fish `generateCompletions` (set to false).
- Add `ff` alias for fastfetch in both bash and fish configurations.

modules/core/packages/appimages/helium.nix

@@ -4,8 +4,8 @@
   fetchurl,
 }: let
   pname = "helium";
-  version = "0.14.2.1";
-  hash = "sha256-JQQ5K+WUZ3ly5mklNPGZWDTlq+mJqqS02oJgC3in5U0=";
+  version = "0.14.3.1";
+  hash = "sha256-umRDXcHlDRDWpdP4wxr81q+cUXkjiIxyg2AcJRFQaMA=";
 
   src = fetchurl {
     url = "https://github.com/imputnet/helium-linux/releases/download/${version}/helium-${version}-x86_64.AppImage";