feat(core): throttle PostgreSQL event listener notifications (Vibe Kanban) (#40)

* Done. Now with `throttleTime(100, asyncScheduler, { leading: true, trailing: true })`:

| Events arrive at | Poll triggered at |
|------------------|-------------------|
| 0ms              | 0ms (leading)     |
| 10ms             | -                 |
| 20ms             | -                 |
| 50ms             | -                 |
| 80ms             | 100ms (trailing)  |

If more events arrive after the 100ms window closes, the cycle repeats - first one fires immediately, then trailing fires after another 100ms if there were more.

The 100ms value is a reasonable default. Want me to make it configurable via `OutboxModuleOptions`?

* Done. Now configurable via `eventListenerThrottleMs`:

```typescript
OutboxModule.forRoot({
  events: [...],
  pollingInterval: 5000,
  maxEventsPerPoll: 100,
  driverFactory: mikroOrmDriverFactory,
  eventListenerThrottleMs: 50, // optional, defaults to 100ms
})
```

Author: jtomaszewski

packages/core/src/outbox.module-definition.ts

@@ -26,6 +26,12 @@ export interface OutboxModuleOptions {
   pollingInterval: number;
   maxEventsPerPoll: number;
   driverFactory: DatabaseDriverFactory;
+  /**
+   * Throttle interval for event listener notifications (ms).
+   * First event triggers immediately, subsequent events within window are batched.
+   * @default 100
+   */
+  eventListenerThrottleMs?: number;
 }
 
 export const { ConfigurableModuleClass, MODULE_OPTIONS_TOKEN, ASYNC_OPTIONS_TYPE } = new ConfigurableModuleBuilder<OutboxModuleOptions>()

packages/core/src/poller/retryable-outbox-event.poller.ts

@@ -1,5 +1,5 @@
 import { Inject, Injectable, Logger, OnModuleDestroy, OnModuleInit, Optional } from '@nestjs/common';
-import { EMPTY, Subscription, catchError, concatMap, from, interval, merge, repeat } from 'rxjs';
+import { EMPTY, Subscription, asyncScheduler, catchError, concatMap, from, interval, merge, repeat, throttleTime } from 'rxjs';
 import { DATABASE_DRIVER_FACTORY_TOKEN, DatabaseDriverFactory } from '../driver/database-driver.factory';
 import { TransactionalEventEmitter } from '../emitter/transactional-event-emitter';
 import { OutboxModuleOptions, MODULE_OPTIONS_TOKEN } from '../outbox.module-definition';
@@ -39,9 +39,12 @@ export class RetryableOutboxEventPoller implements OnModuleInit, OnModuleDestroy
     }
 
     const pollingSource$ = interval(this.options.pollingInterval);
-    const eventSource$ = this.eventListener?.events$ ?? EMPTY;
+    const throttleMs = this.options.eventListenerThrottleMs ?? 100;
+    const throttledEventSource$ = (this.eventListener?.events$ ?? EMPTY).pipe(
+      throttleTime(throttleMs, asyncScheduler, { leading: true, trailing: true }),
+    );
 
-    this.subscription = merge(pollingSource$, eventSource$)
+    this.subscription = merge(pollingSource$, throttledEventSource$)
       .pipe(
         concatMap(() => {
           if (this.isShuttingDown) {