feat(applications): add COSMIC calculator module

modules/applications/by-name/cosmic-ext-calculator/default.nix

@@ -0,0 +1,26 @@
+{ lib, ... }:
+lib.cosmic.applications.mkCosmicApplication {
+  name = "cosmic-ext-calculator";
+  originalName = "COSMIC Calculator";
+  identifier = "dev.edfloreshz.Calculator";
+  configurationVersion = 1;
+
+  maintainers = [ lib.maintainers.HeitorAugustoLN ];
+
+  # NOTE: There is also a history configuration entry, but I will not add it here, since I don't think it belong as a setting, but rather an state entry
+  # It will probably open a PR there, fixing it.
+  settingsOptions.app_theme =
+    lib.cosmic.defaultNullOpts.mkRonEnum [ "Dark" "Light" "System" ]
+      {
+        __type = "enum";
+        variant = "System";
+      }
+      ''
+        The theme of the application.
+      '';
+
+  settingsExample.app_theme = {
+    __type = "enum";
+    variant = "System";
+  };
+}