- Introduced `claudeResponsesUsageTokens` to manage detailed token statistics, including input, output, cache read, and cache creation tokens. - Updated aggregation logic to include cached tokens in total usage calculations. - Refactored usage processing to simplify token merging and ensure consistent handling across streaming and non-streaming responses. - Added unit tests (`TestConvertClaudeResponseToOpenAIResponses_ReportsCacheTokens`) to verify correct cache token inclusion in usage metrics. Closes: #3807