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/auth-service/users_tests.rs

@@ -0,0 +1,70 @@
+use auth_service::users::{hash_password, verify_password};
+
+#[test]
+fn test_password_hashing_and_verification() {
+    // Test with a simple password
+    let password = "test_password";
+    let hashed = hash_password(password);
+    
+    // Verify the hash is not the same as the original password
+    assert_ne!(password, hashed);
+    
+    // Verify the password against the hash
+    assert!(verify_password(password, &hashed));
+    
+    // Verify an incorrect password fails
+    assert!(!verify_password("wrong_password", &hashed));
+}
+
+#[test]
+fn test_password_hashing_with_special_characters() {
+    // Test with special characters
+    let password = "P@$$w0rd!#%^&*()";
+    let hashed = hash_password(password);
+    
+    // Verify the hash is not the same as the original password
+    assert_ne!(password, hashed);
+    
+    // Verify the password against the hash
+    assert!(verify_password(password, &hashed));
+}
+
+#[test]
+fn test_password_hashing_with_unicode() {
+    // Test with Unicode characters
+    let password = "пароль123你好世界";
+    let hashed = hash_password(password);
+    
+    // Verify the hash is not the same as the original password
+    assert_ne!(password, hashed);
+    
+    // Verify the password against the hash
+    assert!(verify_password(password, &hashed));
+}
+
+#[test]
+fn test_different_passwords_produce_different_hashes() {
+    let password1 = "password1";
+    let password2 = "password2";
+    
+    let hash1 = hash_password(password1);
+    let hash2 = hash_password(password2);
+    
+    // Different passwords should produce different hashes
+    assert_ne!(hash1, hash2);
+}
+
+#[test]
+fn test_same_password_produces_different_hashes() {
+    let password = "same_password";
+    
+    let hash1 = hash_password(password);
+    let hash2 = hash_password(password);
+    
+    // Same password should produce different hashes due to salt
+    assert_ne!(hash1, hash2);
+    
+    // But both hashes should verify against the original password
+    assert!(verify_password(password, &hash1));
+    assert!(verify_password(password, &hash2));
+}