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/utils/health_check_tests.rs

@@ -0,0 +1,64 @@
+use reqwest::StatusCode;
+use std::env;
+use std::time::Duration;
+use tokio::time::sleep;
+use utils::health_check::start_health_check;
+
+#[tokio::test]
+async fn test_health_check_endpoint() {
+    // Set a custom port for this test to avoid conflicts
+    env::set_var("HEALTH_CHECK_PORT", "8099");
+    
+    // Start the health check endpoint
+    let result = start_health_check("127.0.0.1").await;
+    assert!(result.is_ok(), "Failed to start health check: {:?}", result.err());
+    
+    // Give the server a moment to start
+    sleep(Duration::from_millis(100)).await;
+    
+    // Make a request to the health check endpoint
+    let client = reqwest::Client::new();
+    let response = client.get("http://127.0.0.1:8099/health")
+        .timeout(Duration::from_secs(2))
+        .send()
+        .await;
+    
+    // Verify the response
+    assert!(response.is_ok(), "Failed to connect to health check endpoint: {:?}", response.err());
+    let response = response.unwrap();
+    assert_eq!(response.status(), StatusCode::OK);
+    
+    let body = response.text().await.unwrap();
+    assert_eq!(body, "OK");
+    
+    // Clean up
+    env::remove_var("HEALTH_CHECK_PORT");
+}
+
+#[tokio::test]
+async fn test_health_check_invalid_path() {
+    // Set a custom port for this test to avoid conflicts
+    env::set_var("HEALTH_CHECK_PORT", "8098");
+    
+    // Start the health check endpoint
+    let result = start_health_check("127.0.0.1").await;
+    assert!(result.is_ok(), "Failed to start health check: {:?}", result.err());
+    
+    // Give the server a moment to start
+    sleep(Duration::from_millis(100)).await;
+    
+    // Make a request to an invalid path
+    let client = reqwest::Client::new();
+    let response = client.get("http://127.0.0.1:8098/invalid")
+        .timeout(Duration::from_secs(2))
+        .send()
+        .await;
+    
+    // Verify the response
+    assert!(response.is_ok(), "Failed to connect to health check endpoint: {:?}", response.err());
+    let response = response.unwrap();
+    assert_eq!(response.status(), StatusCode::NOT_FOUND);
+    
+    // Clean up
+    env::remove_var("HEALTH_CHECK_PORT");
+}