nixos/hypridle: only run the service on Hyprland

`/run/user/1000/hypr` directory is only created if a Hyprland session is active.

`%U` gets the UID of the current user.
Link: https://www.freedesktop.org/software/systemd/man/latest/systemd.unit.html

Finally closes NixOS#347651

nixos/modules/services/wayland/hypridle.nix

@@ -20,11 +20,14 @@ in
     systemd = {
       packages = [ cfg.package ];
       user.services.hypridle.wantedBy = [ "graphical-session.target" ];
+      # Essential package needed for the service to run properly
       user.services.hypridle.path = [
         config.programs.hyprland.package
         config.programs.hyprlock.package
         pkgs.procps
       ];
+      # Should only be started if a Hyprland session is active
+      user.services.hypridle.unitConfig.ConditionPathIsDirectory = "/run/user/%U/hypr";
     };
   };