[refactor] Refactor ChatManager

* Extracted all commands into CustomCommands.cpp
* Moved all chat-related packet handlers into ChatManger.cpp
* Cleaned up redundant includes
* Unified handler naming scheme
* Made all command handlers in CustomCommands.cpp static

src/CustomCommands.hpp

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "CNProtocol.hpp"
+
+namespace CustomCommands {
+    void init();
+
+    bool runCmd(std::string full, CNSocket* sock);
+};