feat(core): expose request IDs on streaming responses

[2830500285]

Summary

• expose x-request-id through StreamResponse.requestId() and AsyncStreamResponse.requestId()
• preserve request metadata across stream mapping and resource-closing wrappers, including after the underlying response is closed
• keep async access non-blocking and retain request IDs from HTTP error responses for exceptionally handlers

Compatibility

The new interface methods default to Optional.empty() and compile to Java 8 default methods, so existing third-party implementations remain binary compatible.

Validation

• ./scripts/lint
• ./scripts/build
• JAVA_TOOL_OPTIONS="-XX:+EnableDynamicAgentLoading" ./scripts/test
• targeted unit and WireMock tests for blocking, async callback, completion, HTTP error, cancellation, mapping, and close paths

Closes #593