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

database-service/README.md

@@ -0,0 +1,111 @@
+# Database Service
+
+The Database Service is a core component of the MMORPG server architecture, providing centralized database access for user accounts, character data, and session management.
+
+## Overview
+
+The Database Service exposes gRPC endpoints that allow other services to interact with the PostgreSQL database and Redis cache. It implements the repository pattern to abstract database operations and provides efficient caching mechanisms to improve performance.
+
+## Architecture
+
+The service is built using the following components:
+
+- **gRPC Server**: Exposes endpoints for user, character, and session operations
+- **Repository Layer**: Implements data access logic with caching
+- **PostgreSQL Database**: Stores persistent data
+- **Redis Cache**: Provides high-speed caching for frequently accessed data
+
+## Services
+
+The Database Service exposes the following gRPC services:
+
+### UserService
+
+Handles user account operations:
+
+- `GetUser`: Retrieves a user by ID
+- `GetUserByUsername`: Retrieves a user by username
+- `GetUserByEmail`: Retrieves a user by email
+
+### CharacterDbService
+
+Handles character operations:
+
+- `GetCharacter`: Retrieves a character by ID
+- `GetCharacterList`: Retrieves all characters for a user
+- `CreateCharacter`: Creates a new character
+- `DeleteCharacter`: Marks a character for deletion
+
+### SessionService
+
+Handles session management:
+
+- `GetSession`: Retrieves session information
+- `RefreshSession`: Updates session expiration
+
+## Repositories
+
+The service implements the repository pattern with the following repositories:
+
+### UserRepository
+
+Manages user data with methods for retrieving users by ID, username, email, or session.
+
+### CharacterRepository
+
+Manages character data with methods for creating, retrieving, and deleting characters.
+
+### SessionRepository
+
+Manages session data with methods for retrieving and refreshing sessions.
+
+## Caching Strategy
+
+The service uses Redis for caching with the following strategy:
+
+- Cache keys follow a consistent pattern (e.g., `user:{id}`, `character:{id}`)
+- Default TTL of 300 seconds (5 minutes)
+- Cache invalidation on updates
+- Fallback to database when cache misses
+
+## Configuration
+
+The service is configured using environment variables:
+
+- `LISTEN_ADDR`: The address to listen on (default: 0.0.0.0)
+- `SERVICE_PORT`: The port to listen on (default: 50052)
+- `DATABASE_URL`: PostgreSQL connection string
+- `REDIS_URL`: Redis connection string (default: redis://127.0.0.1:6379)
+
+## Running the Service
+
+```bash
+# Set environment variables
+export DATABASE_URL=postgres://username:password@localhost:5432/dbname
+export REDIS_URL=redis://localhost:6379
+
+# Run the service
+cargo run
+```
+
+## Docker
+
+The service can be run using Docker:
+
+```bash
+docker build -t database-service .
+docker run -p 50052:50052 \
+  -e DATABASE_URL=postgres://username:password@host.docker.internal:5432/dbname \
+  -e REDIS_URL=redis://host.docker.internal:6379 \
+  database-service
+```
+
+## Integration with External Systems
+
+The Database Service is designed to work with an external database schema management system:
+
+- **Schema Management**: The database schema is managed by an external web application using better-auth
+- **User Management**: User creation and updates are handled by the external system
+- **Session Management**: Initial session creation is handled by the external system
+
+The Database Service primarily provides read access to this data for other microservices, with limited write capabilities for game-specific data like characters.