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/README.md

@@ -0,0 +1,72 @@
+# MMORPG Server Tests
+
+This directory contains tests for all components of the MMORPG server architecture.
+
+## Running Tests
+
+### Running All Tests
+
+To run all tests:
+
+```bash
+cd tests
+cargo test
+```
+
+### Running Tests for a Specific Service
+
+To run tests for a specific service:
+
+```bash
+cd tests
+cargo test --test auth_users_tests
+cargo test --test character_service_tests
+cargo test --test packet_tests
+cargo test --test redis_cache_tests
+cargo test --test get_user_tests
+cargo test --test grpc_get_user_tests
+cargo test --test mock_tests
+# etc.
+```
+
+### Running Tests with Environment Variables
+
+Some tests require environment variables to be set:
+
+```bash
+# Redis tests
+export REDIS_TEST_ENABLED=true
+export TEST_REDIS_URL=redis://127.0.0.1:6379
+
+# Kubernetes tests
+export KUBE_TEST_ENABLED=true
+export TEST_K8S_SERVICE_NAME=database-service
+export TEST_K8S_PORT_NAME=database-service
+
+# Consul tests
+export CONSUL_TEST_ENABLED=true
+export TEST_CONSUL_URL=127.0.0.1:8600
+export TEST_CONSUL_SERVICE_NAME=database-service
+
+# Run tests
+cd tests
+cargo test
+```
+
+## Test Organization
+
+Tests are organized by service:
+
+- **auth-service/**: Tests for the authentication service
+- **character-service/**: Tests for the character service
+- **database-service/**: Tests for the database service
+- **packet-service/**: Tests for the packet service
+- **utils/**: Tests for shared utilities
+
+## Adding New Tests
+
+To add a new test:
+
+1. Create a new test file in the appropriate service directory
+2. Add the test to the `[[test]]` section in `Cargo.toml`
+3. Run the test to ensure it works correctly