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/cargo/demo-crate/src/lib.rs

@@ -0,0 +1,16 @@
+//! Demo crate for Stack.Gallery Registry e2e tests
+
+/// Greets the given name
+pub fn greet(name: &str) -> String {
+    format!("Hello, {}!", name)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_greet() {
+        assert_eq!(greet("World"), "Hello, World!");
+    }
+}