Add `cancelStream` method to allow aborting active requests. Store the current `AbortController` on the client instance
and reset it when the stream completes or is cancelled. Update `ChatView` to call `cancelStream` on close.
Add comprehensive tests for stream cancellation scenarios, including aborting active requests, handling cancellation
when no stream is active, clearing the controller after normal completion, and allowing new streams after cancellation.
fegger
9823761e03
