feat: Refactor Angular client integration and enhance error handling
- Updated `openapi-ts.config.ts` to configure Angular client plugin with error handling option.
- Modified `app.component.html` to use a demo component for displaying pet information.
- Refactored `app.component.ts` to remove direct API calls and integrate with the new demo component.
- Enhanced `app.config.ts` to provide the Hey API client for dependency injection.
- Improved error handling in client utilities and response processing.
- Added new demo component with HTML and CSS for displaying pet information and error messages.
- Updated client generation scripts to support new error handling and response structures.
- Refactored HTTP client usage to support custom injectors and improved error response handling.