Streaming requests aborted prematurely when HTTP timeout is set

[ainilili]

Setting any HTTP timeout makes the client cancel streaming calls as soon as the timer expires, even though the stream is still healthy.

https://github.com/googleapis/go-genai/blob/main/api_client.go#L58-L65

[ainilili]

I’ve created a pull request to fix this issue. #648