Fix: KafkaConsumer crashes with autoCommit=true (swift-server#102)

Motivation:

Closes swift-server#99.

Modifications:

* `KafkaConsumer`: only subscribe to `RDKafkaEvent.offsetCommit` when
  `KakfaCOnsumerConfiguration.enableAutoCommit == false`

Sources/SwiftKafka/KafkaConsumer.swift

@@ -121,10 +121,16 @@ public final class KafkaConsumer: Sendable, Service {
         self.config = config
         self.logger = logger
 
+        var subscribedEvents: [RDKafkaEvent] = [.log, .fetch]
+        // Only listen to offset commit events when autoCommit is false
+        if self.config.enableAutoCommit == false {
+            subscribedEvents.append(.offsetCommit)
+        }
+
         let client = try RDKafkaClient.makeClient(
             type: .consumer,
             configDictionary: config.dictionary,
-            events: [.log, .fetch, .offsetCommit],
+            events: subscribedEvents,
             logger: logger
         )