Fix command registration for external MCC scripts

- Update Roslyn compiler LanguageVersion from CSharp9 to Latest
- Implement ChatBotCommand.RegisterCommand() (was empty)
- Add RegisterChatBotCommand() helper to ChatBot base class
- Add automatic command cleanup in BotUnLoad via UnregisterChatBotCommands()
- Fix external scripts using Handler.dispatcher (CS0176 static via instance)
- Fix AutoTree.cs wrong Initialize/OnUnload signatures (CS0115)
- EntityCount.cs RegisterChatBotCommand() now works with new helper

Co-authored-by: milutinke <441903+milutinke@users.noreply.github.com>
Agent-Logs-Url: https://github.com/MCCTeam/Minecraft-Console-Client/sessions/27fc44b8-50d8-4194-8057-019a29675d4a

MinecraftClient/McClient.cs

@@ -1025,6 +1025,7 @@ namespace MinecraftClient
             }
 
             b.OnUnload();
+            b.UnregisterChatBotCommands();
 
             bots.RemoveAll(item => ReferenceEquals(item, b));