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

tests/database-service/redis_cache.rs

@@ -0,0 +1,16 @@
+#[tokio::test]
+async fn test_redis_cache() {
+    // dotenv().ok();
+    // let redis_url = std::env::var("REDIS_URL").unwrap_or_else(|_| "redis://127.0.0.1:6379".to_string());
+    // let cache = RedisCache::new(&redis_url);
+    //
+    // let key = &"test_key".to_string();
+    // let value = "test_value";
+    //
+    // // Test setting a value
+    // cache.set(key, &value, 10).await.unwrap();
+    //
+    // // Test getting the value
+    // let cached_value: Option<String> = cache.get(key).await.unwrap();
+    // assert_eq!(cached_value, Some("test_value".to_string()));
+}