fix(transport): resolve SSE stream timeout in JdkHttpTransport (#1322)

Close #1302

This PR fixes `JdkHttpTransport` streaming behavior for long-running
SSE/NDJSON responses, especially LLM streams with long
Time-To-First-Token (TTFT). Previously, JDK `HttpRequest.timeout()` used
absolute timeout semantics for streaming requests, which could terminate
healthy long-lived streams. In addition, blocking stream reads and
error-body reads could run on the JDK HttpClient callback path, and
cancellation/timeout did not reliably close response bodies in all
intermediate states.