Split TeamspeakConnection into focused collaborator classes

Extract notify-event handling and the native-style server log/sound
announcements into ConnectionEventHandler, and getconnectioninfo
request/response + stats-snapshot building into ConnectionStatsCollector.
TeamspeakConnection remains the public facade (1828 -> 1037 lines); its
external API is unchanged. Pure refactor, no protocol/timing changes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

ts3-client/core/src/test/java/com/ts3client/net/EventFieldsTest.java

@@ -9,7 +9,7 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 /**
- * Pins the ts3j behaviour {@code TeamspeakConnection.has(...)} exists for: a field
+ * Pins the ts3j behaviour {@code ConnectionEventHandler.has(...)} exists for: a field
  * the event never carried reads back as an empty string, so a null check would treat
  * every partial update (someone muting, say) as if it reported every other field too.
  */