test: migrate test suite from Jest to Bun test framework

- Convert test files to use Bun's test framework and mocking utilities
- Update import statements and test syntax
- Add comprehensive test utilities and mock implementations
- Create test migration guide documentation
- Implement helper functions for consistent test setup and teardown
- Add type definitions for improved type safety in tests

package.json

@@ -30,11 +30,13 @@
     "@types/node": "^20.11.24",
     "@types/sanitize-html": "^2.9.5",
     "@types/ws": "^8.5.10",
+    "@xmldom/xmldom": "^0.9.7",
     "dotenv": "^16.4.5",
     "elysia": "^1.2.11",
     "helmet": "^7.1.0",
     "jsonwebtoken": "^9.0.2",
     "node-fetch": "^3.3.2",
+    "openai": "^4.82.0",
     "sanitize-html": "^2.11.0",
     "typescript": "^5.3.3",
     "winston": "^3.11.0",