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

auth-service/README.md

@@ -0,0 +1,94 @@
+# Authentication Service
+
+The Authentication Service is responsible for user authentication, session validation, and account management in the MMORPG server architecture.
+
+## Overview
+
+The Authentication Service provides gRPC endpoints for:
+- User login and logout
+- Session validation and refresh
+
+It communicates with the external database service to verify user credentials and manage sessions.
+
+## Architecture
+
+The service is built using the following components:
+
+- **gRPC Server**: Exposes authentication endpoints
+- **Database Client**: Communicates with the database service for user data
+- **Session Client**: Manages user sessions
+- **Password Hashing**: Securely handles password verification
+
+> **Note**: User registration and password reset functionality are handled by an external system.
+
+## Service Endpoints
+
+The Authentication Service exposes the following gRPC endpoints:
+
+### Login
+Authenticates a user and creates a new session.
+
+```protobuf
+rpc Login(LoginRequest) returns (LoginResponse);
+```
+
+### Logout
+Terminates a user session.
+
+```protobuf
+rpc Logout(LogoutRequest) returns (Empty);
+```
+
+### ValidateToken
+Validates a JWT token.
+
+```protobuf
+rpc ValidateToken(ValidateTokenRequest) returns (ValidateTokenResponse);
+```
+
+### ValidateSession
+Validates a session ID.
+
+```protobuf
+rpc ValidateSession(ValidateSessionRequest) returns (ValidateSessionResponse);
+```
+
+### RefreshSession
+Refreshes an existing session.
+
+```protobuf
+rpc RefreshSession(ValidateSessionRequest) returns (RefreshSessionResponse);
+```
+
+
+
+## Configuration
+
+The service can be configured using environment variables:
+
+- `LISTEN_ADDR`: The address to listen on (default: "0.0.0.0")
+- `SERVICE_PORT`: The port to listen on (default: "50051")
+- `LOG_LEVEL`: Logging level (default: "info")
+
+## Running the Service
+
+### Local Development
+
+```bash
+cargo run
+```
+
+### Docker
+
+```bash
+docker build -t auth-service .
+docker run -p 50051:50051 auth-service
+```
+
+## Integration with External Systems
+
+The Authentication Service integrates with:
+
+- **Database Service**: For user data storage and retrieval
+- **Session Service**: For session management
+- **External Auth System**: The service is designed to work with an external authentication system (better-auth) that manages the database schema and user accounts