feat(translator): improve error handling and response conversion for incomplete statuses

- Enhanced response handling to support `response.incomplete` events across translator components and executors.
- Refactored `resultErrorFromError` to centralize error conversion and consolidate repeated logic for constructing custom errors.
- Updated handling of `max_output_tokens` and similar terminal reasons in OpenAI and Gemini translator workflows.
- Introduced `IsRequestScoped` and `IsRequestScopedError` to differentiate between request-scoped and non-request-scoped errors.
- Added comprehensive test cases for incomplete responses, terminal failures, and error propagation in both streaming and non-streaming conditions.

Closes: #3055