feat(tests): add unit tests for accounts and transactions APIs

- Updated package.json to include Vitest for testing and added necessary devDependencies.
- Created accounts.test.ts to test the accounts API endpoints for listing and retrieving accounts.
- Implemented setup.ts to reset test data before each test run.
- Developed transactions.test.ts to cover creating, updating, and deleting transactions through the API.
- Added vitest.config.ts for configuring Vitest with appropriate settings and coverage options.

package.json

@@ -6,9 +6,17 @@
     "dev": "astro dev",
     "build": "astro build",
     "preview": "astro preview",
-    "astro": "astro"
+    "astro": "astro",
+    "test": "vitest",
+    "test:coverage": "vitest run --coverage"
   },
   "dependencies": {
     "astro": "^5.7.5"
+  },
+  "devDependencies": {
+    "@types/supertest": "^2.0.12",
+    "@vitest/coverage-v8": "^0.34.6",
+    "supertest": "^6.3.3",
+    "vitest": "^0.34.3"
   }
-}
+}