Add tests for runStreamJsonSession and enhance session handling
- Implement tests for runStreamJsonSession to validate user prompts and message handling.
- Improve session termination logic to ensure all active runs are awaited.
- Log user prompts with additional metadata for better tracking.
Implement control request handling and refactor related functions
- Added `handleIncomingControlRequest` method to `StreamJsonController` for processing control requests.
- Created `input.test.ts` and `session.test.ts` to test control request handling.
- Refactored `runStreamJsonSession` to delegate control requests to the controller.
- Moved `extractUserMessageText` and `writeStreamJsonEnvelope` to a new `io.ts` file for better organization.
- Updated tests to ensure proper functionality of control responses and message extraction.
