refactor: Enhance GenerationJobManager with In-Memory Implementations

- Introduced InMemoryJobStore, InMemoryEventTransport, and InMemoryContentState for improved job management and event handling.
- Updated GenerationJobManager to utilize these new implementations, allowing for better separation of concerns and easier maintenance.
- Enhanced job metadata handling to support user messages and response IDs for resumable functionality.
- Improved cleanup and state management processes to prevent memory leaks and ensure efficient resource usage.

packages/api/src/stream/implementations/index.ts

@@ -0,0 +1,3 @@
+export * from './InMemoryJobStore';
+export * from './InMemoryContentState';
+export * from './InMemoryEventTransport';