Enable cuda systemFeature in raccoon and fox

This allows running derivations which depend on cuda runtime without
breaking the sandbox. We only need to add `requiredSystemFeatures = [ "cuda" ];`
to the derivation.

m/module/nvidia.nix

@@ -6,4 +6,9 @@
   hardware.graphics.enable = true;
   nixpkgs.config.nvidia.acceptLicense = true;
   services.xserver.videoDrivers = [ "nvidia" ];
+
+  # enable support for derivations which require nvidia-gpu to be available
+  # > requiredSystemFeatures = [ "cuda" ];
+  programs.nix-required-mounts.enable = true;
+  programs.nix-required-mounts.presets.nvidia-gpu.enable = true;
 }