starship: condition nushell integration on nushell 0.73+

Older versions are not supported: https://starship.rs/#nushell

modules/programs/starship.nix

@@ -80,6 +80,14 @@ in {
   };
 
   config = mkIf cfg.enable {
+    assertions = [{
+      assertion = cfg.enableNushellIntegration
+        -> versionAtLeast config.programs.nushell.package.version "0.73";
+      message = ''
+        Nushell integration for starship requires nushell 0.73 or later.
+      '';
+    }];
+
     home.packages = [ cfg.package ];
 
     xdg.configFile."starship.toml" = mkIf (cfg.settings != { }) {