Chest Boat Patch

I've been meaning to get around to this for a while. I kinda had to relearn how Fabric handles client and server code. Found out the hard way that they finally separated the main and client directories/classes finally. Anyway, here are the changes:

• Updated to support 1.21 and above.
• Fixed the version string substitution in fabric.mod.json
• Moved all code from main to client.