Add unit tests for models and services

- Implemented unit tests for the Package model, covering methods such as generateId, findById, findByName, and version management.
- Created unit tests for the Repository model, including repository creation, name validation, and retrieval methods.
- Added tests for the Session model, focusing on session creation, validation, and invalidation.
- Developed unit tests for the User model, ensuring user creation, password hashing, and retrieval methods function correctly.
- Implemented AuthService tests, validating login, token refresh, and session management.
- Added TokenService tests, covering token creation, validation, and revocation processes.

test/fixtures/npm/@stack-test/demo-package/index.js

@@ -0,0 +1,9 @@
+/**
+ * Demo package for Stack.Gallery Registry e2e tests
+ */
+
+module.exports = {
+  name: 'demo-package',
+  greet: (name) => `Hello, ${name}!`,
+  version: () => require('./package.json').version
+};