feat: implement lazy singleton pattern for repository instances and update related imports

src/data/repositories/lazy_singleton.ts

@@ -0,0 +1,7 @@
+export function createLazySingleton<T>(factory: () => T): () => T {
+  let instance: T | null = null;
+  return () => {
+    instance ??= factory();
+    return instance;
+  };
+}