refactor: Enhance GenerationJobManager with improved subscriber handling

- Updated RuntimeJobState to include allSubscribersLeftHandlers for managing client disconnections without affecting subscriber count.
- Refined createJob and subscribe methods to ensure generation starts only when the first real client connects.
- Added detailed documentation for methods and properties to clarify the synchronization of job generation with client readiness.
- Improved logging for subscriber checks and event handling to facilitate debugging and monitoring.

packages/api/src/stream/interfaces/IJobStore.ts

@@ -112,6 +112,9 @@ export interface IEventTransport {
   /** Get subscriber count for a stream */
   getSubscriberCount(streamId: string): number;
 
+  /** Check if this is the first subscriber (for ready signaling) */
+  isFirstSubscriber(streamId: string): boolean;
+
   /** Listen for all subscribers leaving */
   onAllSubscribersLeft(streamId: string, callback: () => void): void;
 }