Extracted preferences & entity stubs to make them reusable

tests/stubs/Entity.ts

@@ -0,0 +1,17 @@
+import StorageEntity from "$lib/extension/base/StorageEntity";
+
+export interface TestedSettings {
+  stringField: string;
+  numberField: number;
+  nested?: {
+    field: boolean;
+  };
+}
+
+export class TestedEntity extends StorageEntity<TestedSettings> {
+  static readonly _entityName = "entity";
+
+  constructor(id: string, settings: TestedSettings) {
+    super(id, settings);
+  }
+}