Fair Sophisticated Backpacks

Simple mod that give you a Slowdown 4 effect (-75% movement speed), whenever you have more than one backpack of any type in your inventory, on the back or anywhere else. It also applies to any entity you are riding (horses etc.), although it doesn't currently work for custom vehicles that may use different movement mechanics.

Please issue a ticket on github, if you wish for me to make it for example for 1.20.