Update flake.lock and Helium version

Refactor nix settings to use a flat `nix.settings` structure and rename
`nixPath` to `nix-path`.

modules/core/packages/appimages/helium.nix

@@ -4,8 +4,8 @@
   fetchurl,
 }: let
   pname = "helium";
-  version = "0.18.3.1";
-  hash = "sha256-xDrhTCq3FVWz/kC9Al3wBPcLxHlalhoaOlaXn6G4uYA=";
+  version = "0.19.2.1";
+  hash = "sha256-oEVQo8fHC9rTrNOkQw7ajSr8C/cXOpxYpAP+q5UXCH8=";
 
   src = fetchurl {
     url = "https://github.com/imputnet/helium-linux/releases/download/${version}/helium-${version}-x86_64.AppImage";
@@ -37,4 +37,3 @@ in
     };
   }
 # https://github.com/imputnet/helium-linux/releases/download/0.11.7.1/helium-0.11.7.1-x86_64.AppImage
-