[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/NPCManager.cpp

@@ -6,7 +6,6 @@
 #include "ChunkManager.hpp"
 #include "NanoManager.hpp"
 #include "TableData.hpp"
-#include "ChatManager.hpp"
 #include "GroupManager.hpp"
 #include "RacingManager.hpp"