Add comprehensive documentation and unit tests

Documentation:
- Add detailed README files for all services (auth, character, database, launcher, packet, utils, world)
- Create API documentation for the database service with detailed endpoint specifications
- Document database schema and relationships
- Add service architecture overviews and configuration instructions

Unit Tests:
- Implement comprehensive test suite for database repositories (user, character, session)
- Add gRPC service tests for database interactions
- Create tests for packet service components (bufferpool, connection, packets)
- Add utility service tests (health check, logging, load balancer, redis cache, service discovery)
- Implement auth service user tests
- Add character service tests

Code Structure:
- Reorganize test files into a more consistent structure
- Create a dedicated tests crate for integration testing
- Add test helpers and mock implementations for easier testing

packet-service/src/auth_client.rs

@@ -69,10 +69,7 @@ impl AuthClient {
         Ok(response.into_inner())
     }
 
-    pub async fn logout(
-        &mut self,
-        session_id: &str,
-    ) -> Result<Empty, Box<dyn std::error::Error + Send + Sync>> {
+    pub async fn logout(&mut self, session_id: &str) -> Result<Empty, Box<dyn std::error::Error + Send + Sync>> {
         let request = LogoutRequest {
             session_id: session_id.to_string(),
         };