Update greeting message to HELLO

[Copilot]

This PR updates the main greeting message in the MapleStory packet parser application from "Hello from maplestory!" to simply "HELLO" as requested.

Changes Made

• Modified the main() function in main.py to print "HELLO" instead of "Hello from maplestory!"

Testing

The change has been tested to ensure:

• The program runs successfully with the new greeting
• All existing functionality remains intact
• The packet parsing and hex-to-text conversion features continue to work as expected

This is a minimal change that only affects the initial greeting message while preserving all the core functionality of the MapleStory packet analysis tool.

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