- Update DeepSeekHandler to support prompt caching
- Add cache token tracking in usage metrics
- Update DeepSeek model configurations with cache-related pricing
- Enhance test coverage for cache and usage metric handling
- Add OpenAiHandlerOptions interface for configuration
- Extract processUsageMetrics to base class for reuse
- Update RequestyHandler to extend OpenAiHandler
- Add proper type safety for metrics handling
- Clean up code duplication across handlers