docs: add comprehensive testing guidelines for Laravel Cycle ORM Adapter

Created .cursor/testing-guidelines.md with detailed guidance for testing
the Laravel-Cycle ORM bridge functionality:

🎯 Key Features:
- Bridge-focused testing philosophy and patterns
- Docker-first workflow with native PHP alternatives
- Multi-database testing strategies (SQLite, MySQL, PostgreSQL, SQL Server)
- Real-world examples from current test suite
- Integration testing patterns for Laravel services

📚 Comprehensive Coverage:
- Test organization and structure documentation
- Entity/Repository testing patterns with real entities
- Service Provider and Laravel integration testing
- Console command testing with output verification
- Database testing strategies and custom assertions
- Laravel service integrations (Cache, Queue, Session, Telescope)

🛠️ Practical Examples:
- Complete test implementation examples
- Docker command reference for all scenarios
- Troubleshooting guide for common issues
- Best practices with DO/DON'T patterns
- Performance optimization strategies

🎯 Target Audience:
- New developers joining the project
- AI assistants working on the codebase
- Contributors needing testing guidance
- Maintainers ensuring test quality

This comprehensive guide enables effective testing of Laravel bridge
functionality while maintaining code quality and project standards.

Author: lotyp